Awwww, poor girl. She probably only needs to be outside with them because they are too lazy to train her house manners. People irritate me, any dog can be trained to be inside, they are mans best friend and want to be close and please. I have never had personal experience with mastiffs but I hear they are pretty laid back dogs. One of the guys my mom works with had to go to a house that owned one and the dog never even barked, he had to actually step over the dog who only lifted his head and wagged his tail and laid back down. He was only a couple of years old. The owner told him he was very mellow. Now maybe that was just that dog? Good luck in whatever you decide. Just follow your heart.