Did you have any idea of where you wanted to go with this idea?
The first thing I thought when I read your story was that she was like an "extra" in someone else's dream space, like this world she was in wasn't even real.
Alternatively a wish could have been used against her to rob her of any social rapport.
Either one has a lot of potential... Imagine if Karen and Jon were the ones to make the wish, but it inadvertently affected them too and they started to forget her too. Lots of potential for Sarah to be very devious if everyone just forgets about her shortly there after.
Anyway, just some ideas that went through my head.
