Deanna --
I'm assuming you've been giving the combination of meds for a while. The only thought I had was whether there's any indication of an interaction between any of Billie's meds. it may be a matter of separating some of them by a few hours. You're not cutting the Kepra, are you? (It's time released and shouldn't be split.) If most of Billie's meds are also human meds, your pharmacist may be able to tell you about interactions.
Also, you noted Billie has food allergies. Can you take a very close look at the labels on her food. Manufacturers frequently change the formulation of their food and unless you're reading the labels routinely, you never know when this happens. (They sometimes make changes and don't let us know, as well, given how poorly regulated the pet food industry is.) Perhaps keeping track of any changes in respiratory rate and what Billie is eating may help to figure out if a food allergy is the culprit. And if your weather is anything like ours, it's a miserable time for allergy sufferers.