Sounds like a typical case of co-dependance. many many people have this. I do. Working on it right now.Its a mixture of low self-esteem, being confused about your identity, not having your emotions validated by those you grew up around, and the overwhelming fear of rejection and abandonment.
The catch 22 is that to be in a relationship like this can make you resent them and bring about their own self-fulfilled prophecies of rejection.
But, unless she is ready to admit to herself she has these issues and has the courage to face them she will remain trapped.
Here is a link with some info:
http://www.allaboutcounseling.com/codependency.htm
I wish her all the love in the world - because it probably feels inside like even that won't be enough right now.
Swerve