We adopted a lab/pointer mix puppy last week - he is 5 months old and his name is Granger (as in Hermione Granger from Harry Potter!). He is very stand-offish to DH and DS but loves me (his mom!) and his sisters DD's 15 and 20. So I am really hoping he warms up to the boys! I believe in some cases dogs know but could also be that the person reminds them of a negative experience (or could be your SD is a $hit). I think there is a chance Granger had a bad experience with men - I don't think he was ever abused but definitely prefers women. We will be investing in training too! Good luck and congratulations on your new addition!

How old is this dog? Is it a rehomed one?  If the latter, it may have been mistreated in its previous home by a child of similar age and sex.  That's all I can think of.   If it's a very young puppy it just needs some good training out of bad habits. 

Our dog has always disliked men, particularly teenagers to 30s. I got him as an 8 week old pup. There are a few guys he likes -DH, my dad, my uncle - and sometimes he'll warm up to a man, but for the most part he doesn't like them, even those I'd consider to be of good character.

I would venture to guess that it's more of a dominance thing. The dog is trying to figure out where this small human lands in the pecking order.

Yes.  It is my understanding, or so I have heard, that dogs can sense intent.  I had a dog (Max) once that was pretty much nice to everyone, except for when a male friend of mine would come over.  Max would snap and growl at him no matter now much I tried to get him to stop.  Not much later, I found out this "friend" had a, let's say, weird sexual obsession of sorts over me.  I dropped him ASAP as even a friend, of course.  But, my dog Max knew all along!

It likely is where she falls in pack order I'd say.  That said, you said this a couple times, why on earth are YOU paying for everything related to SD?  What about your DH? It's his kid.  Does BM not pay CS also?  You better change that situation really fast.

When no one is looking ?   Or pushing the puppy away ect.  The dog does  not like her There must be a reason for that. The puppy likes everyone else 

I truly believe animals have a much keener sense about people than we do.  They don't have the complex communication abilities like we do (words, conversation) so I think they are still very hard-wired to this sense.

Whether they pick up on our anxiety or they form their own around certain people, I believe their behavior speaks volumes.  If an animal is hostile, anxious or afraid of someone - pay attention. 

My (late) dogs would have absolutely nothing to do with SD.  In fact, one of them used to go into the basement and stay there for the duration of SD's visits.  The dog didn't do this with anyone else.   I found it to be very telling.  

My dogs LOVE my SD and go ape sh*t when they see her.  That said, that's because she doesn't live with us, is older and our relationship is at a VERY wonderful place after years of torment, torture and misery.  I wonder if they would have felt the same if she lived with us and was younger.

I will say, she is NOT an evil person, but she definately had major issues with authority and mini-wife syndrome.  She constantly competed with me.  She was very feral in many ways as BM didn't care to raise her at all.  She however has done well.  She has a job, she lives w/her boyfriend and his family now.  She graduated.  She IS nice to animals and has always been nice to mine.  Even my cats and previous dog really liked her.  Pissed me off because I couldn't stand looking at my dog girl snuggle up to her LOL. 

A dog on leash just tried to eat the head of my parent's dog. The poor little guy lost his L eye and nearly his life when he was attacked.  No, animals are not good judges of character. They are animals. Not people.

That said, some dogs can certainly decide if someone is a threat.  Not that I see that as a dog making a judgement on the character of a person.

Sounds like the puppy is trying to establish his place in the pack packing order. He thinks he is more important than the SD and trying to be dominant to assert his position in the pack. He will learn if SD feeds him or is allowed to do things he cant ... he needs to learn to accept he is below a child in pack hierarchy that's all :) 

My dog is above my skids. In fact so are my tortoises LOL. Kidding but only partially.