Hello, welcome to Just Answer. What a wonderful thing that you and your husband did by adopting this kitten and taking her into your him. I understand how loud and persistent she has become with her crying out, and you are correct in thinking that her yowling and behavior is due to her heat cycle. Female cats can be quite annoying when they are in heat, and there is very little to do to stop the noise. I also think your veterinarian is correct in wanting to wait for the infection to clear up before spaying her, as we always want to minimize the risk to our patients before putting them under anesthesia or through a surgery. Fortunately, the behavior is temporary, so either the infection will clear and she can undergo surgery, or she will come out of the heat cycle soon in order to restore peace and quiet in the house. In the meantime, if her noise is unbearable, I would suggest boarding her at a pet facility or at your vet's office if they will permit it. That would keep her safe, prevent a pregnancy, and allow you to have a quiet household again for a bit. I hope that helps, good luck!