Cats suddenly started fighting

I got my 2 cats Jada (spayed female) and Jack (neutered male) at the same time about a year and half ago and they are now about 2 years old. They have always gotten along very well, until recently. Jack is acting more assertively (or aggressively) towards Jada. I think he just wants to play, but she isn't interested. For the past two weeks she has been living under my bed, not coming out to eat, drink or potty. I had to start bringing the food, water and litter box into my room, shut the door and coax her out from under the bed. When Jack gets near her, she starts growling and hissing. What should I do?

Welcome to TCS!

At the point in which Jack became more "aagressive" towards Jada - did anything change in the house? Did either of them leave the house (like to go to the vet)? Did you bathe one or the other? Has there been a strange cat hanging around outside? Did any family visit?

They had both been to the vet for their annuals. I called the vet a few days after this started happening, and they suggested that Jada might still smell like the vet and it upset Jack. They told me to get a piece of clothing that I had worn and to rub it on Jack and then on Jada. This didn't seem to help. Nothing is new in the house that I can think of, and I haven't noticed any cats outside. They've never been bathed, and no one has been over. Thanks for the response.

It was probably the change in smells that caused Jack to act aggressively towards Jada. I would try a re-introduction - but I can't find the link I want right now to be useful! Basically, keep them separated. Start in a few days switching bedding (towels they sleep on or blankets). Let them sniff each other's bedding. After maybe a week or two, try letting them out together & watching them closely. Hopefully, someone else can find the link I want - or try searching the forums for "re-introduction".