Hello,
Generally, the next 24 hours after a vaccine is given, most cats will be a bit lethargic/ sleepy and not quite themselves. The vaccine is stimulating their immune system, which can be overwhelming to them. It is expected.
Signs that this is more than just the expected reaction would be complete unresponsiveness, vomiting more than once, or this continuing past tomorrow. For now, I would not worry with her present condition. I would let the vet know on your next vaccine visit, however, that she does get sensitive to them, and if more than once vaccine is due, it is best to spread them out, giving just one, then going back in a week or two for the other.
Hope this helps, but let me know if you have further questions by just replying.
Christine
Certified Veterinary Technician
Licensed veterinary technician (B.S. Mercy College), 10 yrs in animal medicine and training
We're happy to help, and I wish you and your cat nothing but the best. Take care,