I get the impression that she didn't strain to pee, is that right? If so, I doubt it's a UTI, but never the less, you should take her to a vet to rule it out.

Perhaps she sensed you were going out, and wanted to tell you to stay home. Fister once went up on our bed and made a poo when we had visitors and was about to sit down to eat! I'm glad it was hard poo, so I could just take the blanket off and leave it till later. When a cat want to tell you something, they'll find a way.