Min pin

Hello, I just picked up my MinPin from the humane society,she is 5 years old and a very affectionate dog. Our only problem is is the 1st day we took her home she peed on my rug. I thought s he was excited. Then again a couple of days later.after that we closed off the dinning room this way we could keep an eye in her. Then she seemed okay, NOW for the past week she will walk off into the bathroom and pee but only at night and after we take her out. Today 7/20 she just let herself off the couch and went in the bathroom and peed again.She ran back into the living room like a child would when they did something wrong, so I went as soon as she came back to us to check and then reprimanded her and put her in her cage.i know I may sound silly but I know she knows what she is doing because of her actions. I raised many dogs large & small and never had a problem like this please help. :---)