Okay, this is wierd, but it sounds very similar to what my food allergies sometimes do to me.

Can she try an "elimination" diet? Start, for example with just some hamburger and rice, a little bit, see how that goes ... if she throws up that, try lamb or venison (if it's available ...) In other words, try simple ingredients to see if you can find something that doesn't upset her stomach.

NO snacks or treats while this is going on, until you figure out safe ones.

Also, does she bolt her food? That can exacerbate a delicate tummy ...