...She goes after him the moment she sees him and has nipped him many times on the hands, face, etc. When I say a stern "Ah-Ah" whenever she nips him, I can see that she feels bad about it by her body language, but she goes back to doing it within the next few seconds (the same even if I use repellents)...
..Since she is remorseful, it means she just hasn't learned what is too much and what isn't...
Hi Jacob, sorry to hear you're having some troubles with your pup and the kiddo.
I pulled out these two snippets above, as a springboard for comments about a common misconception people often have, about dog behavior.
You say you "know" she "feels bad" and this other poster uses the word "remorseful," but really...she is just a puppy and this is not really how dog brains work.
I guess I would ask you why you feel she "feels bad"? Does she slink or cower? Lower her head? Curve sideways and move off a bit? Stop making eye contact?
All these are appeasement, or "calming" gestures--part of dog body language and a way to let you know she feels stressed and would like you to back off with whatever you're doing that makes her feel stressed.
It's NOT that she is experiencing the human emotions of shame or remorse--she's a baby dog and she is reacting to your body language, your tone of voice, and your verbal correction.
Think about it--the very fact that she continues to go right back at the kid demonstrates she just doesn't get it, yet.
I highly recommend this book, for reading her canine signals: On Talking Terms with Dogs: Calming Signals,
It's only about ten bucks, is an easy read, packed with great info and great photos to demonstrate the ideas in the book, and worth its weight in gold, truly.
Yes, like said above I would not let the dog free roam the house at all. Leashed or crated at all times.
And find a professional.
Yep. You said she goes after kiddo when she first hears him on the stairs. Since that behavior is highly predictable--that's the prime opportunity for you to be proactive and totally prevent it.
Here's a free web article you might find useful, as well: Bite Inhibition Article