Its funny she didn't try to escape in recent years although it was mentioned that she still has the maturity of an 11 year old girl. Also I guess some girls are very "girly" and also she had the daughters with her. As I think her step father mentioned - maybe not trying to escape saved her life
Also I don't know what it was like living with such weird unstable people like her abductors and she was probably spending all her time trying to look after the children...