I have no idea why, but about 6 weeks ago our female Golden retriever, Cider, began acting tense, and slightly aggressive to our youngest child, a 9 year old boy. She will curl her lips and sometimes give a slight growl when he tries to pet her, unless someone else is near being a "chaperone", but even then she goes very tense, and I can tell does not want him near. I do not believe there was any negative incident to bring this on, and she will still play with him outside and romp around, but when its time to be calm and affectionate, she does NOT want it from him. We have tried some different things, and haven't had much success. She did just come into heat for the first time a couple days ago. Not sure if hormones are messing with her, but its completely exclusive to him. Any ideas or experience with this, what to do to help them become great friends again?