So, Riley and your daughter's other male are both good around all other dogs, just not each other?
It could have been an issue with them both biding for attention from your daughter and both trying to claim dominance in her house.
First, bring them both together on NUETRAL territory, like a park or something. One person holding each dog on a leash, let them take turns smelling ech other hind ends -
no face to face.
After they've sniffed each other for a minute, take them on a walk together, a good long walk. If either one starts to get agressive to the other while walking, give a quick tug on the leash but keep going. Try to make it somewhere that will be intersting enough for both dogs so they don't pay too much attention to each other, but at the same time they "share" the experience. Make it a controled walk for both dogs, no leash pulling, zigzaging etc., just walk.
After the walk, take them both somewhere that they can both explore together, but NOT you or your daughter's house - nuetral territory.
I'd do this a few times until they can do it without giving each other even any "dirty looks". Any time they do, correct it immediatly by putting them both in a "sit" or "down" and stand in between them. Wait for them to be totally calm, then try letting them interact again.
When you feel like they can both be in your daughter's house at the same time, start ouside, keep it controled, don't let them just rush to each other. Don't let the dog coming in run into the house and also don't let the dog that's already there rush to the door.
Something made them decide they had to fight for dominance, getting them both back on the same "level" and you and your daughter as the "alphas" is what needs to happen. As was mentioned, you may want to look into a professional trainer to help you and help "read" their body language and signals to stop and correct the behavior before it escilades. I personaly wouldn't yell at them if they're fighting, that's for the most part, only going to add to their "excitement" level and make it worse. You need to physicaly separate them and get them both calm, nothing verbal except maybe one
quick loud noise to get their attention.
Good luck
