My dog is doing her business on the carpet! how do I make her stop?

I just recently moved to this apartment that had cats that did their "business" on the carpet. The night before I was moving into my new apartment she went #1 on my rug in my living room. She never did this before even as a puppy. I do take her for walks everyday when I come home from work. We do walk close to about 1 mile. I then move into my cat filth apartment after the rugs were shampooed. About a week later I found #1 and #2 on the rug! as I said everyday rain snowing etc I make sure she gets walked no matter what except if she's sick you know what I mean. I did clean it up and sprayed the stain and the entire living room with Natures Miracle. Then the same night I was watching TV in my room, she did #1 in the living room!! I did the same thing again only this time spray a lot of it on the carpet and did rent a carpet shampooer. I can't let her go into my living room without her going to the bathroom on the rug! what should I do? I'm very worried about my dog. She is 5 years old and she is a Boxer. I did ask the vet she said it might be the odor in the rug that makes her think there is another animal in the house but there's not. Please help! serious answers please! Thanks!