is she being left alone for an extended amount of time? i have read that cats can sometimes have separation anxiety and show it by peeing on things even if they've never done it before.
she's likely to have a UTI. hopefully you'll take her to the vets BEFORE it becomes worse - the pain of this can be unbearable for a kitty.
it's simple to clear up with antibiotics and some shots for pain relief if it's in the early stages. you'll probably have to feed her a special diet you can buy from the vet (hills science diet)...for at least a few months. you should be feeding your cat the best food you can afford anyway.
please take her to the vet before she starts peeing blood!
once the infection clears up she will be just as well behaved as she was before.
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