Anytime someone is diagnosed with something of this type, there's a lot of mental adjusting to do-especially when you're young and thought you had a lot more years left before any chronic health conditions popped up on your radar.
If you really want to help her out, I have two suggestions-one, try to avoid giving her any medical information. It's tempting to help her understand her condition, but if you say anything that could be misconstrued in any way at all, or doesn't match EXACTLY what her doctor already told her, then you could throw her into a panic and make her mistrust her doctor (and having a solid, trusting relationship with her doctor is one thing that she really needs right now). If she asks you to explain something, just encourage her to ask her doctor.
Second, suggest she see a qualified health psychologist. These are counselors specially trained in the psychology of health and illness, and they frequently counsel newly diagnosed patients of all kinds. My aunt freaked out when she was diagnosed with breast cancer, and her oncologist referred her one-she said it was very different from "regular" counseling and it really focused on getting comfortable with her diagnosis, not letting it disrupt her life, and developing a positive attitude.