I would tell her, "you may not like cats, but I love them. We can agree to disagree, okay? Let's talk about something else."

If she persists, tell her that cats have been human companions for thousands of years, have have their images on walls in the pyramids of the pharoahs in Egypt. Cats saved humanity from the bubonic plague by killing the rodents that were carrying it throughout Europe. And while you don't expect her to love them, she can at least respect that some people do.