She could stay and try to subdue him while The Faceless struggled to take control back. It had a chance of working, even a slight one, and it would at least leave Dipper an nonviable host.

Or she could run. She could get out of a situation that just a moment ago looked like certain death. She could find a way to undo this not just for Dipper, but for every member of The Legion.

She could leave him behind.

Part of her thought it was cowardly but the overwhelming part of it recognized it as just common sense. If anything went wrong in attacking him, that was a much lower chance of putting things right.

"I'll get you out of this! I promise! I'll think of something!"

She was going to wonder if this was the right thing to do until this whole thing was over, but still she turned to run.