I don't think it has anything to do with her son being a "stranger", I brought my Tom up from a poult and have handled him and fed him from my hand constantly. Now at 6 months old he is very territorial towards me to keep me away from the hen. I never thought this would happen with me spending so much time with him and handling him every day. So I am not sold on the "stranger", I just thinks he in particular is a threat that he may be appealing to the hen...just my opinion.