Hmm… well you did state that Betsy has a UTI… maybe she's just in pain and doesn't feel like walking?!! I had a diabetic cat, and before he was diagnosed he had continuous UTI's. He would pee everywhere around the house, and the vet stated that animals think that wherever that they "GO" is why it hurts, so maybe she's afraid to go pee outside because it's hurting her.
I agree that the socialization could be the issue as well… is she fearful of other dogs?!! or animals?!!