I've been through something like this before.
She's had a pop tart and a malt because you lose all desire for traditional foods. Then you see something like a malt or a pop tart that has emotional appetite stimulation and you're so glad you actually want to eat something that you do it.
For me it was sweet potato pie, fries, and bacon. Show me a regular food, and it was like looking at a pile of bathroom tiles on a plate.
I would say more likely than not that what she has is not life threatening.
In my case, it was a mind over matter issue. Stress had gotten the better of me without even knowing I was under stress. Didn't want to eat anything, and when I did it would be like that alien exploding out of dude's chest in Alien.
She needs a doctor, and on your end, examine what her life has been like recently. You never know. Can't hurt. Regardless of whether or not a doctor is involved, the doctor will likely ask these questions anyway, so it helps to be prepared to answer them as accurately and completely as possible.
For now, follow the basics of human health. Make sure she stays hydrated and is resting as much as possible. But get to a doctor ASAP.
DO NOT hesitate to go to the emergency room if things start to get real hinky. I lost and uncle to " no we don't need the emergency room, it will be fine" and nearly lost my left eye surrendering to the same foolishness. Not saying it is or will get that serious, but simple problems can spiral out of control in minutes.
Best wishes to her, and you'll both be in my prayers.