Challenging dominant behavior is very typical of a mastino. Not so much in females though. We are trying to help, not be harsh- but your situation demands harsh, swift behavior. Find a good trainer. Fast. Any fear that your fiancee displays will only make these situations worse. There are a few things you can work on in the meantime. Not letting her on furniture. At all. You walk first through doors. She doesn't tell you when she feels like being petted- you tell her. YOU are the boss- not her. You give a command, she does it- PERIOD. If not, force her. And only give a command once. Don't allow her off lead. Ever. Avoid walking in the woods until you consult a trainer if this is the only place it happens.