I have a 12 week old female rottweiler puppy. She is aggressive when playing in the house. She always wants to teeth or bite. She often starts growling and then bites. She has drawn blood when biting my girlfriend. We researched online and tried several of the mentioned remedies like yelling ouch when she bites too hard or putting her in time out. We don't even like trying to pet her because she wants to start biting. When she is tired or just wakes up she is an angel. Not sure what to try next. Any suggestions?