Herself

She jumped up, startled. "nobody else should have a key for here" she thought, as she turned to look into her own face.
The intruder, (the real Jill)looked just as startled as she was.
"Who, are you???" They both started in unision, "I'm Jill Weston..........." they continued before traling off. "You can't be I'm Jill .... No I'm Jill"
Both starting to recount things from their childhood to prove which one was real,but this was to no avail as the new Jill (James) had been briefed so well by Sadie, on her life believing her to be the real Jill that both now had near identical memories of their childhood, their whole life.