I agree, it sound likes she might have a UTI. Stash had one, and he also peed on me several times while I was in bed under my blankets. The vet will give her liquid oral meds, and it should clear up.
PS- never heard of a cat going into heat after getting spayed, usually when the uterus is removed, the hormones that make them going into heat are removed(the uterus holds almost all hormones). I would also mention that to my vet. Sounds a little off. GOOD LUCK with Kitty. Hopefully it isnt anything serious.