"Fergus is dead?"
She didn't want to believe it, she couldn't believe it. And despite her vow to herself to never show weakness, she could feel the impending breakdown. After being beaten and burned by Lucifer, left feeling helpless, she didn't think she could handle much more. Her son, her only son, was dead, and despite her feelings of hatred for him, there was also love, love that was buried long ago by hatred, love that was now threatening to show in the face of grief.

"I hate you because if I didn't, I would love you."

"Yeah," Sam said, and Dean added, "Killed himself to save us."
Rowena couldn't stop her voice from shaking. "That doesn't sound like him at all."
"Well, Fergus-I mean, Crowley-he changed a lot," Sam explained. "He came through in the end. I think you would've been proud of him."
"Is that so?"

"I always knew my boy was meant for big things."

She would deny it until the day she died for good, but she was indeed proud of him. She had never in all her years expected her little boy would one day become the King of Hell. She most certainly would never have expected him to die the way he did.
It took everything she had to keep from breaking down, to keep her sobs at bay, but no matter what she did, she could not stop her voice from shaking.
"Fergus was my only child." Her voice raised. "And I promise you, I would rather have a living son-even if he hated me-then a dead hero!"
She didn't look at them, but she knew they were shocked. And why wouldn't they be? She had tried to kill him several times. But despite that, he was her son, and a part of her would always love him, even if she didn't want to admit it.

"Love-love is a weakness. And I'll never be weak again."

She felt very weak right now though.