House Trained Dog Peeing In House?

My housetrained 11 year old dog is starting to pee in the same spot in the house. She had a UTI a few weeks ago and had recovered, but now that we allowed her back in the house she has peed in the same spot twice in three days. She does when we are home, when she could have easily let us know she needed out. I am wondering if she smells it even though I have thoroughly shampooed the carpet and that is causing this. Any thoughts or ideas on the subject would be appreciated. Thanks!