I’d just try to reaffirm her reasons for wanting to be a doc, remind her how she’s going to be an amazing physician, encourage her, and remind her that no matter what happens (the worst case being she’d need to apply again) that you’re there for her and support her.
For me the worst part was not knowing what was going to happen, and my hubby reminding me it would all turn out, that it was OK if I had to apply again, and that he supported me no matter what... that helped me immensely.