It definitely could be a stroke. About all that can be done (and truthfully, a vet can't do much more) is keep her quiet, offer "high value" (in flavor and calories) food in small amounts, try to ensure she stays hydrated (a syringe of unsalted or very lightly salted broth, or rehydration solution frequently) and see how she does.
If they want to give her a chance, helping him stand (a piece of cloth or clothing under her belly as a sling works well) several times a day, and ensuring that she isn't always lying in the same posistion is important.
Her reluctance to eat may be due to nausea from whatever is causing her circling (and it could be something as simple as an ear infection or fluid in her ear), OR it could be she's having difficulty swallowing due to partial paralysis.
If she doesn't improve in 2-3 days, the chances of recovery go down badly.
Oh... have them check her carefully all over for a tick. There is a thing called tick paralysis, and it's fatal... But can be reversed if caught early. And the most important part is getting rid of the infected tick.
Summerthyme