Yikes.

It's sad how people think Goldens and Labs are all super sweet dogs and get along with everyone, and then you see all these dogs turning on you or other dogs. There was a 5mo purebred Lab puppy at our dog park once and he kept attacking the other dogs. I even had to pull her off another dog once because the owner was too far away to grab her when it happened.. And I remember this other time, a couple was leaving with their two black Labs, when one of them suddenly attacked a GSD/Rottie mix, and held on to the back of the dog's neck and wouldn't let go! Luckily, no dog ended up being hurt... But it makes me upset to see a breed that was once known for its great temperament go down the hill because of the problem of overbreeding and irresponsible breeding.

You said you purchased the dog from a BYB at work? Have you told the breeder about the litter's health and temperament problems? Are they still breeding dogs? You should complain to the breeder, and maybe even make the breeder help pay if your dog needs surgery for hip dysplasia or whatever... It is the breeder's responsibility and fault that the dogs ended up like that. If they had been more educated, and bred their dogs responsibly, your family dog probably wouldn't have ended up like that.

This is also the reason why I don't like people buying dogs from backyard breeders.. Then you end up with a dog with who knows how many problems and you have to deal with it. I've learned this too. Megan, my Pom (mix?), came from my aunt, who BYB her BYB girl dog to my grandma's petshop puppy. Now Megan has had two surgeries to removes stones from her bladder, and she has to be on a special diet for the rest of her life. The vet said it was probably due to bad genes. To tell you the truth, I didn't even want Megan and Monica in the beginning... I had been begging my parents for a Border Collie or Aussie, and then my aunt literally handed the two pups over to us without even my mom's say in it. However, my aunt was nice enough to actually donate $200 to help me pay off Megan's surgery.

Okay, so after having blabbed so much, I realized I haven't even answered your question...

Honestly, I don't really know how to help ease aggression. Monica is pretty aggressive towards dogs she doesn't know.. What I've been doing with her is taking her on walks, and just getting her used to seeing other dogs and correcting her if she starts barking and wanting to go after the dog. In your case, it's like a family matter... So, my advice - Maybe try to figure out what the source of the aggression is? What seems to trigger her being aggressive? And maybe go from there... Or does she just attack for no reason? Why does she get along with one dog and not the rest? Have you tried properly introducing her to your other dogs?
I think maybe consulting a behaviorist would be a good idea...

Good luck!

Edit:
After giving birth, Megan and Monica's mother also died...
I've been planning on taking Monica to the vet to make sure she doesn't have what Megan has...
*sighs*