I'm merely speculating because of a line delivered by Glados. She did have Chell's file: An unlikable loner. Like by no one. Very formal. Very official.
Well, at the same time we've come to learn that almost everything that comes out of Glados seems to be complete lies, especially when Chell escaped being "Baked."
Glados obviously was saying that stuff about Chell to agitate her.
As for who Chell is personally, we don't know since not enough info is given about her. I think she's merely a Volunteer tester who survived in her cubical chamber when Glados went postal (love the cut emergency phone-line in the boss fight chamber) and awoke years later.