Note: Snape's daughter was born in 1979, so she's a year older than the Golden Trio.
"Albus, I will not allow this!", Severus exclaimed at Dumbledore. "She is sixteen years old!"
Dumbledore nodded solemnly. "I am aware of her age, Severus, but the Death Eaters are expecting her to join soon. Draco Malfoy, as well."
Maria Snape listened from outside the door.
Join the Death Eaters?
When she heard movement from the office, Maria quickly ran around the corner; a safe distance away to not be caught eavesdropping.
Her father exited the headmaster's office and motioned for her to follow.
"How much did you hear?", he asked.
"What do you mean?", Maria feigned innocence. She was quite good at that.
"Maria, we both know that you were listening. How much did you hear?"
They entered Snape's classroom.
"Dumbledore wants me to be a Death Eater", she said quietly.
Snape nodded. "Yes. I don't want it any more than you do."
"Isn't it my choice, though?", Maria asked, beginning to pace around the room. "Don't I get any say in this?"
Snape sighed. "I am afraid not."
"What do they want me to do?"
"They want you to listen to the next Order meeting, and report it back to them.", Snape replied.
That's easy. "I can do that."
"That's not all", her father continued. "After you do this, Bellatrix wants to give you the Dark Mark personally."
Maria's eye widened. "No. No, I'm not letting that crazy b-", she caught herself. "I'm not letting her near me!"
"If you don't do this, it will look as if I let you become a part of the light side. I need you to do this."
Maria sighed. "Fine, I'll do it."
So, she was dragged to the next Order meeting, listening at the door since she was "too young" to be in the actual meeting, according to Molly Weasley.
Maria had managed to lose Potter, Granger, and the Weasley kids-she wasn't a Ravenclaw for nothing-and was alone.
She made mental notes of everything that was said; knowing well enough not to write anything down in case someone found them.
"What are you doing?", a hushed voice made her jump.
It was one of the Weasley twins-who can tell them apart?-was staring at her with an accusing look on his face.
Whatever you do, don't tell anyone anything
"I was thinking of a plan to sneak into the kitchen. I'm starving."
Fred/George seemed to understand. "You could always call Kreacher, he probably won't do anything for you, though."
Maria smiled.
"You should probably come upstairs", the twin said, "If anyone catches you you'll be in a lot of trouble."
No kidding, Maria thought bitterly.
She followed him up into the room that the others were in.
"Hear anything, George?", the other twin (Must be Fred) asked.
"Nope", George replied.
The group talked for awhile before Granger leaned in to Maria and asked, "You're Snape's daughter, right?"
Maria fought the urge to roll her eyes.
No, I just look exactly like him and have the same last name. Crazy coincidence, right?
She nodded at the bushy-haired witch.
"Does he tell you any of what's going on down there?", Potter asked.
Maria shook her head. "Nope", she lied. "I don't know why. I mean, I'm almost of age!"
The twins snorted. "Tell us about it."
In reality, Severus told his daughter quite a bit of what the Order talked about, but only because he had taught her Occlumency when she was young.
There was a knock at the door and Mrs. Weasley opened it. "Maria, your father is leaving soon."
She nodded. "Okay, I'm coming."
Once they had apparated home, Snape asked, "How much did you hear?"
"I know what the weapon is, where it is, and why the Dark Lord wants it", Maria recited.
Snape gave her a smile. "Good."
The next Death Eater meeting came too fast for Maria's liking.
She reported everything, praying that her voice wouldn't waver or break.
Bellatrix cackled once she was done.
"Look at that!", she shrieked, "Ravenclaws are good for us!"
"Come, dear", she grabbed Maria's arm and pulled her out of her chair.\
No one told her the Dark Mark would hurt.
"Congratulations, Snape", Bellatrix sneered as she came back to the table. "Your little girl's one of us now."