Is my cat in heat or having a UTI?

Hello, this is my first post on this forum however I am completely stumped as to what is going on with our kitten. We have 2 kittens that we adopted in February 2016. Both are females. About a month ago we adopted a female puppy. So far, the cats seem to be getting along great with the puppy. About 2 weeks ago one of our cats starting howling and crying like crazy and peeing all over our house, in our plants, on our beds. We took her to the vet who said that it is most likely a UTI. We got her a new bigger litter box, put her on antibiotics and switched her to C/D food. She got better in 3-4 days. I did mix in a little bit of her old food into her new C/D food because she wasn't eating. About a week later, her symptoms came back. She was peeing on our bed and crying like crazy. We then decided to throw out the tiny amount of old food we were giving her and kept her only on C/D. Now, it is over a week later and she is STILL sick. We went out of town for the weekend and got back yesterday and she was acting very strange... she peed on our bed, she was rolling around the ground like crazy to the point where we thought she was losing her mind, she's walking around with her butt and tail up, licking herself constantly, she is making all these weird growling noises, howling, crying constantly. Lately we noticed that she's been trying to escape our apartment more and more when typically, that is not something she ever did. She is being extremely affectionate to the both of us, rubbing herself on us, licking, biting etc. She's being very affectionate toward the cat too. Now, the peeing would be consistent with a UTI however I feel like all the other symptoms are pointing to a cat in heat. The rolling around, the growling, noise making, escaping, affection etc. Is it possible the shelter didn't spay her properly or at all? Also, is it possible that the peeing her marking her territory since there is another female cat in the house? Or am I being crazy? 

She is still using her litter box and never cries in the litter box. It's always when she's walking around our apartment. She did meow and make some noises when she was peeing on our bed. 

We have an appt to take her to the vet tomorrow but I did want to see if anyone had experienced this before or thinks that I might be right that she is going through heat right now? Is it possible she had a UTI and now is in heat? She's about 11 months old right now.

Thank you!

Dominika 

Yes, it's possible they missed a bit of ovarian tissue, so she could be in heat. Ask the vet to run a hormone test.