This was the only way. She knew she had to keep Tina, Jacob, and Newt safe as best she could, she knew that they could take care of themselves, but this was the only way to get on the inside of Grindelwald's plans, get him to trust her and take him down from the inside.
Yes, she might die tonight. But she knew that she was the only one who could trick him, convince him she had really switched sides. Anyone that was going to join him had to be convincing. He has to believe it. And she's the only one who can do it, she's the only one who can fool him.
Grindelwald thinks that he's invincible, that his weak and feeble shield of Occumency would be able to keep her out. He thinks that she is someone who can be manipulated, played with, discarded. He thinks that she's disposable, that Jacob isn't useful or needed, that Tina has no potential and that she's violent and a murderer. He's wrong and she was going to be the one to show Grindelwald that.
Jacob's final cries to her rang through her head.
"You're crazy."
Crazy
CRAZY
Crazy
Crazy
Maybe she was, maybe this was insane, but she had to do it. She meets his eyes and knows that he means it. The words he hadn't spoken aloud before but did now. She looks at her sister and sees her heartbreak, feeling her own heart shatter as well. Three more steps, two more. She steels herself against the flames.
Queenie Goldstein stepped into the bright blue flames, letting out a scream of anguish as she did so. She focused on the thought that she actually supported him. Terrified that the flames were going to consume her.
"Queenie!" Tina's cry carried over the room, worry ringing in every letter, and Queenie choked back a sob and another scream. Reminding herself that she was doing this for her sister, for Jacob, for Newt, and the rest of the people she knew and cared for.
She crossed the last of the flames and walked towards Grindelwald. He held out a hand and she took it, stealing her features and letting a mask fall over her. Now she wants to join Grindelwald, she really does, because she knows that that is the only way to save them.
Stealing one last glance at her sister, who would probably never forgive her, Queenie closed her eyes and lifted her head to the ceiling, with one thought on her mind I'm sorry Tina, please forgive me. and let the black and white smoke whisk her away into the uncertain future that awaited her.