I have a black lab mix who is about two years old. she is the love of my life, and we have her mom and a half sister from another litter. I like to play fight with them all, like they do with eachother... but the other day i took her over to our neighbor's house (who has a german short hair that is almost 4) and instantly after he came to see her she started growling and trying to bite him. I'm planning on having other dogs some day outside of her family and i don't want this to happen again. so i was wondering if she was just trying to protect me or what?

Seeing as we were not their to witness what exactley happened, we cannot say why she growled.
But if I were you, I would get in contact with an animal behaviorist and get some help, if it was aggression.

where would i look for one? i live in a small town and i love my dog but we really don't have the money to spend hundreds of dollars on one animal since we have 3 dogs, a cat, a frog, and a lizard.

I would ask your vet for recommendations on animal behaviorists. I wish that I could give you a site that lists a bunch, but I have yet to find one. If I do, I will post it though.

I think the problem with your dog has to be with socialization. There was not enough information in your post to make an accurate diagnosis.
From your post it looked like your dog spent most of it's time in a certain pack (you and your other dogs). When another dog (or person) came in contact or close proximity your dog did not like that.
Socializing a dog does not mean you let your dog sniff other dog's privates. Socializing your dog means you need to introduce your dog to social situations. You will need to have your dog on a leash. Your dog needs to be sitting at your left side (basic obedience 101). Then another person with their dog on it's leash will be brought up to you on your right side. You will need to keep you dog at your left and in a sit. You can let your dog look but it should remain in a sit-stay the whole time the other dog is on your right. You will need to praise your dog for remaining sitting on your left during that period. You should repeat this training.
Progress is made when your dog loses interest in the other dog that is sitting on your right. Eventually, you should be able to pet the dog on your right and still have your dog in a sit at your left. When your dog is doing good do not forget to praise your dog.

The fight may not have been started by your dog although it looked that way to you, or it may have been started because of a problem with human intervention via a leash. Dogs generally get along best on neutral territory, rather than at one of the dog's homes, especially when they can meet off leash. There's a great book that is mostly pictures with descriptions by Turid Rugaas about calming signals. That's a cheaper place to start.

I would be very careful with dogs being off leash. If both dogs get into a fight and if the fight extends to the handlers getting bit. If there is a court case...and your dog was determined to be off leash and demonstrated prior bad behavior....See what I mean?