Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today.
In regards ***** ***** question, we do need to tread with care.
From her history, it sounds like she may have a bacterial or inflammatory gastritis from handling those mice even if she didn't eat them. Of course, we'd have to be wary if there could have been a fourth one that she did eat (and perhaps filled her enough that she didn't eat the others). With this in mind, as long as she has no belly pain, her gum color is normal, and she is able to keep water down; we can try some home supportive care for her. To start, if she hasn’t just vomited (since otherwise we’d need to rest her stomach for a few hours first), then you can consider treating her with an antacid. Common OTC pet safe options would be: Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid) or Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet). Whichever you choose, we’d give this 20 minutes before food to allow absorption. Of course, do double check with your vet if she has a known health issues or is on any medications you haven't mentioned. Though if you give this and she cannot keep it down due to nausea that is usually a red flag that we need to bypass her mouth with injectable anti-vomiting medication from her vet.
Afterwards, you can consider starting her on an easily digestible diet like boiled chicken, boiled white fish, scrambled eggs, or meat baby food (as long as its garlic/onion free). There are also OTC vet diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity) too. The aim of these diets is that they will be better tolerated/absorbed by the compromised gut. Therefore, it should get more nutrients in and result in less GI upset. And if we are concerned that a fourth mouse could be possible, we can add canned pumpkin and OTC cat hairball treatment to her food to help push any bones/fur through the gut. As long as improvement is being seen, I usually advise continuing this until the signs are settled, and then weaning her slowly back to her normal diet.
Since dehydration is a risk for vomiting cats, we need to keep an eye on her hydration. To check that she isn't dehydrated, there are a few things you can test. Further to checking for gum moisture, do make sure she doesn’t have sunken eyes and that she doesn’t have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then that would be our cue to have her seen before this becomes an additional issue for her (especially as it is often dehydration that makes them feel unwell).
Overall, we do need to tread with care for your lass. So, we’d want to start supportive care to settle her stomach. If she cannot keep that or water down at any point, appears dehydrated already, or doesn’t respond to the above within 12-24 hours; then we'd want to get her vet involved. They can assess her hydration, check for the above and start or injectable anti-vomiting medication, fluids, +/- antibiotics to get her settled before this can take a toll on her.
All the best,
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