Happy Pee

We have a dog that is around 6 months old... well my roommate does. She never took the time to truly potty train her once we rescued her from the pound. BUT she has a problem of peeing when you tell her to come to you. She will run to you and sit and pee or get near you after you call her and creep and pee. She will be laying on her back and will pee as well. I dont know how to stop this and it is getting pretty bad. You cant go to pick her up off the couch without her peeing .. please tell me how to help this issue out!