I'm having a Ripleys Believe or Not Moment.
Hmmm...you're not feeding it *frozen* are you? That is to say, you're defrosting it and just feeding it "cool" right? I'm assuming you are. If that's the case, my thought is that - there are some tummies (in humans too) that can be, oddly, sensitive to temperature (does she ever vomit after colder water, btw?). Have you ever let the raw frozen sit until actual room temperature and given it then?