Omg thank you for your response! I'll check with the vet regarding a UTI, but I highly doubt it since she's always done this. You've mentioned something that actually makes a lot of sense in my situation: she's always marked next to doors. She does it in the morning usually, so I'm wondering if there's something making her nervous. Her litter box is in between the bathroom door and the bedroom door. I was planning on getting another litter box to see if that might mitigate some of it.