She transforms mentally

Sarah was about to agree with Tom when she felt an odd feeling. It was the same tingling that had changed her, only like it was inside her brain...

Her memories started getting replaced by Samus's memories.

There was a buzzing in Sarah's brain, and suddenly she could remember. The memories were vague, she remembered being on a ship with Tom, one that was going down with only one escape pod left. Weeks in close confines with her that had turned to passion. She remembered marrying him after a year of relationship.