Maybe offer to go with her to her first appointment to the doctor or counselor? If she doesn't go, you should go any way - you will learn where you need to draw the line for your own sake. Depression doesn't just affect the person diagnosed with it, it affects those around them too and you'll need to know where and what your role is in all of this. You can't take the role as savior - no one can do that - this is something she will need to work through and something you'll need to work through as well as you discover how you can best help her.
Hugs,
Einna