She experiences herself through others' reaction to her

 

It is too burdensome to shoulder herself.  She places that burden onto others.  Others' reaction to her determines her worth.  She does everything to make that reaction favorable because that tells how valuable she is.

If everyone were nice, she is OK.

Did you blame her a lot when she was younger?

Remind her to value herself.  Her worth is not determined by what others think of her, but by her courage and willingness to shoulder herself.

It is not easy for a young girl, or even grown ups, to say to herself: I am responsible for myself, my happiness rests on my own shoulders.

If she derives her happiness from helping others, that is OK.  But she needs to be clear as to what is actually motivating her; she needs to be conscious of this: I am helping is because that person needs the help, or, I need to help someone in order to feel valuable?

With that clarity, she will attend her own need first (so that she does not put extra burden on you (the mother) and on the person she is helping.)