Story inspired by the fans who feel Maggie should be the one to punish Negan, if the show goes in that direction. Besides that, I haven't really seen any fics of Maggie contemplating Glenn's death or confronting Negan about it.
Title is Negan's own words from the season 7 finale when he noticed she was alive.

"What's the right thing Glenn?"

She held the pocket watch and gently ran her fingers over it as she stood over his grave. She had been thinking about her husband a lot lately. She'd seen him in dreams, always smiling at her and wordlessly telling her he loved her. A common dream was him standing next to her as the doctor told them how well their baby was doing on the ultrasound. Maggie never looked at the screen; she had only kept her eyes on Glenn.
She curled her fingers around the watch as her eyes began to moisten. Then she rested a hand across her belly. Several of the Hilltoppers had said it was a miracle the war hadn't stressed her to the point where she'd totally exhaust herself and lose the baby. It hadn't been an easy fight, but they had survived…they had won.

They had...won.

Won?

Her fingers curled harshly into the pocket watch. It hadn't felt like a complete win if she was honest with herself. Partially because so many had died, but the main reason was because their main target had managed to escape. Thinking about it only made her feel as though she'd lost Glenn all over again.

"Maggie."

She turned as Rick walked up to her. Ever since the war ended, he never seemed capable of looking at her the same way. There was a clear look of admiration for her strength, but there was also the expression of shame.

Rick blamed himself for Negan's escape and had apologized, but no matter how many times she told him it wasn't his fault, he didn't appear to believe it. No one blamed the man, but as leader, she knew it was natural to carry the weight of guilt.

"Find anything?" she asked. He shook his head in response and she dropped her head in disappointment. "Okay."

Ever since the war ended, small groups had gone out on a manhunt hoping to bring the bastard to justice. Rick had gone out every time, nearly dying on two occasions. Asking him to sit one out was pointless.

"We're gonna find him, I promise."

She gave him a false smile and rested a hand on his shoulder.

"I know." It was a lie. She was certain Negan was probably long gone from the area. Such a thought made her stomach twist even more than it had on the day he vanished.

The Hilltoppers weren't completely right about her. She wasn't holding up all so well. She was in the beginning, but afterwards, she felt her strength was evaporating slowly. With so many eyes on her she had to play strong. She refused to be looked at as a poor widow who couldn't move on from the past after all. Of course she would never forget Glenn, but as of late his loss felt so fresh.

"I will," Rick promised again.

"You should take it easy," she said softly as she noted the dark circles under his eyes. "You can't push yourself to-"

"I have to…" he drifted off as his eyes fell to the grave. "For Glenn, I owe him, and everyone that he killed. We won't make it unless it's done."

Maggie started to speak, but then her thoughts drifted to the Governor, specifically the time when he returned—and killed her father.

Without realizing it, a tear was running down her cheek.

"Oh, Maggie, I'm sorry if I—"

"No, no it's fine." She felt that sickening twist in her stomach that had arrived the day she saw her father being held hostage.

But it wasn't fine. She thought about Beth next. Beth turned into Glenn, who turned into her father, who turned into Beth, who became Sasha. It was a sickening cycle of the people that had left a sense of hollowness within her. She had always managed to push past it. She had made sure to push past it, for the sake of the baby, for the sake of living. She wondered sometimes if she was truly living.

"It's not fine. You need this to be done, we all do."

"It won't bring him back," she said shakily.

"But it will give us closure. You deserve that. You've been, amazing through all of this. I don't know how you've done it. I'm not sure if I could."

Maggie wiped the tear away, and in doing so noticed a few passing Hilltoppers in the distance tossing her a concerned look.

"Sometimes I don't feel like I can anymore. Sometimes I don't feel like, I'm the person everyone sees. I am trying."

She didn't want to give up. She didn't want to feel crushed whenever she saw some ghostly image of Glenn smiling at her. There had been moments, though very few, where she felt the strong need to join him where ever he'd gone. She would be with the rest of her family.

"It's okay to hurt. You don't have to be strong all the time."

"Sometimes…I keep seeing Glenn." She met Rick's eyes, fearful of sounding crazy, but Rick was giving her a look of understanding as he nodded for her to continue. "Been happening a lot lately. In my dreams mostly. I don't know what it means. Maybe I'm going crazy, or maybe it's a sign I can't take it anymore."

"I don't believe that," Rick said firmly, yet softly. "When I lost Lori, I saw her everywhere. I thought I was going crazy, maybe in a way I was. It's not a sign of going crazy, or a sign that you can't make it."

"Then what is it?"

Rick bowed his head as a flash of grief passed over his features.

"A sign of how much you need him. How much you miss him."

Her eyes fell to the mound of dirt again.

"I do need him," she whispered.

"Rick!"

They both looked up to see Jesus running toward them. Both readied for the worst.

"Rosita's group is back, and they…they got him."

Neither needed clarification on what he meant. Right away, Maggie felt as if something had burst inside of herself.

"Dead? Is he dead?" she immediately asked.

"No. They managed to bring him back alive."

Rick exchanged a look with Maggie before following Jesus. She hesitated briefly, before hurrying after them.

The majority of the community was there, blocking a clear view of Rosita and Dwight and the few others that had gone with her. Maggie quickly moved through the crowd with one thing on her mind.

"I have to see…let me see," she muttered.

When she made it to the front, she saw him. The bastard was being pulled out of the back of the car, hands bound behind his back. He stumbled and shook his head in a manner that suggested he'd been knocked around a bit or even knocked out. Two men that had been a part of the hunt, including Dwight, held their guns on him.

"How?" Rick asked simply.

Rosita tossed a look at Dwight.

"Thanks goes to him, mostly. He thought of a place we should check a second time. We ambushed the son of a bitch."

"Why didn't you kill him?" Maggie practically demanded, her voice suddenly raw.

Rosita stared back at her for a few good minutes before answering.

"I tried to once. I thought someone else deserved a shot. If I couldn't bring him back, I would have."

Maggie turned her attention to Negan who was slowly beginning to acknowledge what was going on. She was certain there was a brief flash of fear, before he brought up a smile.

"Now this is what I call a goddamn welcome party, and all for me."

"Shut the hell up," Rosita warned.

"Rick," Maggie said quietly without turning to face him. Negan, on the other hand, turned his attention to her, still smiling.

"Well, if it isn't the dead widow. Always a fucking pleasure to see that beautiful face."

"I swear to god." Rosita had her gun out in a flash and was jamming it into his neck.

"Do it! Kill the bastard."

"He deserves it."

"It should be Rick."

"I want to do it!"

Maggie gazed around at the rising blood lust of the crowd. The war had strengthened them to the point where they no longer wished to back-down the way Gregory had wanted them to. They were fighters now, fighters desiring revenge.

She looked at Negan and wondered what could be going on in his head. He gave no clear expression; he was simply watching the vocal crowd. Rick looked to her and Maggie raised a hand to quiet them all.

"We won't do it here. Take him back to Alexandria and lock him up, til we decide when and where." He turned to Maggie then. "You agree?"

She gave a nod.

"Ezekiel's people will want to be there for it."

"So I guess that's it then," Negan spoke up. "No life behind bars. Just put on a good show of dying."

Rick stepped forward, glaring hard.

"You deserve it."

A silence followed, then Rosita signaled for the men to place him back in the car. Maggie quietly watched the scene unfold feeling numb. Suddenly images of Glenn being struck with the bat plagued her mind. She stumbled back as she saw his bloodied face in her head and shut her eyes. She pressed a hand over her belly and held back the tears.

"You okay?"

She looked up, not even realizing Rick had come up to her.

"I will be, when this is done."

I planned for Negan to be dealt with in one way, but I'm open to another form of punishment that can be exacted if anyone has one, otherwise Negan's fate is sealed next chapter.