Update: She had a bad reaction to the booster and got all the meds she needed today and is already on the mend. Thanks for all the well wishes, I'll post more of her here soon.
Brought her to the vet on Friday, and I think she picked something up from there, and we got her booster shots that day just to avoid just this scenario. Anxiety isn't allowing me to relax until we get her feeling OK, but I have an appointment set for tomorrow, so here's hoping. So yea, send her all the well wishes please if ya don't mind.
Edit: thanks everyone for the kind comments, we love and appreciate you all.
Glad to hear your cat Cleo is doing better, fam!