So you took your dogs to her house, one of her dogs growled at one of yours and your other attacked? Seems like your dog may have had a reaction to protect your other dog, which growling triggered.
You have to be careful taking your dogs into someone elses property. While some dogs are fine with it, others are more territorial. There are also certain things that set off another dog – my dog has issues with more ‘alpha’ dogs and certain breeds (boxers and pits it seems).
If your dog gets into a fight, reaching into it is the worst thing you can do. You need to remain calm for starters (I know hard, but it’s definitely recommened) and try and have two people. You both grab the rear legs of the other dog and walk back. The dog can’t get around to bite you, and you can separate them. If there is just one person, you are supposed to leash one carefully, tie it to something, then pick the other dogs rear legs up and walk back.
Your friend is in the right to call animal control, and depending where you are located (unsure which country/state), they may have different reactions. Honestly, if you were my friend and you invited me over and this happened, I wouldn’t report you. The thing is, the dogs got into a fight, it happens. Reaching into it was the first bad move your friend made – really puts them at fault for getting bit (if she really did).
Animal control where I am is pretty good about this – we’ve had several dog fight bites due to owners reaching in and all of them ended in 10 days of not leaving the house, needs to be on a leash, and a visit from animal control to check all tags and vaccines.
Don’t call them yourself, but do call/email/text your friend to check up on them. You want to see how the dog is and how they are and if there is anything you can do. Just throw the offer out there. My dog got into a scuffle with another dog and the lady that broke it up did the same and ended up getting a small bite. I followed up with her to make sure she was fine and told her to let me know if she had to get medicial attention or anything. She didn’t report it, and actually only wrote me one response back and just ignored my other emails to her. I was pretty annoyed, as I was trying to be responsible, but let it go.
On another note: If you want your dogs to meet for the first time, take them out of the house and do on leash meetings on neutral ground. This is the best way to introduce new dogs. We always do this when bringing a friends dog over to our house for the first time.