How do you get your girlfriend to have confidence in herself?

Thank you for caring about her self image. You are a kind person.

Poor self image is a common problem but fixing it is something that takes time and skill. She can only gain confidence by succeeding at things she fears failing at, and those things are often very deep and long lasting - maybe she herself cannot say what they are.

There is no quick answer that a stranger on a website can provide and probably not a lot you can do to help her. If she wants help, a therapist of some sort would be useful.