Long time reader, first time poster!
I have a six year old girl with somewhat aggressive tendencies towards other dogs, but she never bites and after a very exciting five second face off when meeting new dogs, she usually gets on great with them. Not a huge problem, just leads to a lot of time explaining and reassuring other dog owners. Never bitten anyone, and she's extremely friendly to all humans.
My mom has a 1.5 yo male Basenji (her nephew as it happens) which was treated like her own son for most of his life - he was allowed to "breastfeed" from her, he was never punished for biting or being too rough, and quite frankly us humans were much harsher with him than she was.
UNTIL his testes dropped. Now all of a sudden she can't stand the sight of him, and not only growls whenever he comes near, but she'll leap out of the couch and chase him halfway around the room if he dears to come up to her while she's sleeping.
This isn't all the time of course, sometimes she'll deign to eat next to him, she'll even sleep next to him at times, but only after showing him who's boss.
Of course, the little pup is confused as hell about this, and not only misses his "mother", but really wants to play with her. And this creates no end of troubles for us, since we spend a lot of times together at holidays and such, and this has been an issue for about six months now with no improvement in sight.
I wonder if sterilization would help, but obviously it would have to be her, and that's not only expensive, but dangerous and here in Norway it's not easy to get the vet to do it, since they're very careful about it.