My girlfriend is depressed and getting worse, what do I do?

She started out being sad over mistakes in her past, and I tried to rationalise her choices to make her feel better. However I now realise this won't work. She feels guilty if I tell her that I love her. She feels like she doesn't deserve me. Therefore I often tell her that she makes me happy, we recently came to the conclusion that even if she thinks she doesn't deserve me, if she breaks up with me then it will make me unhappy which is exactly what she doesn't want.

We are in a long distance relationship, in other countries, so I cant just sit there or hug her.

We have spoken about therapy and she wants to go. But what can I do or say to her to help her through this