Eight month old female pitt mix puppy does not eliminate outdoors?

Please help me with my rescue dog. Her name is Jasmin and she came from a neglectful home, where very little training was done with the dog. She is a great puppy, and can be trained for the most part... Except... she REFUSES to go outdoors. I let her out around the same times during the day, and she wanders around on her leash sniffing and will sometimes pee. But, as soon as she comes back in and plays with our other dog, she squats and poops either in our bathroom or behind our sofa. She doesn't understand when we tell her no. She just keeps wagging her tail. I think she wasn't paid any attention, so anytime we give her negative or positive, she just sees it as attention. Please please help me. I really like her, she is a sweetheart! But we can't keep a dog that uses our apartment as a toilet. Please help us!