Why does my dog growl at other dogs when they try to sniff her?

It sounds like she needs some social skill training. My daughter has a new lab puppy and she took him to a basic dog training class to teach him manners and to let him become familiar with other dogs. The class was wonderful. Her instructor told her dogs sniff each others butts to greet each other basically the same way humans say hello or shake hands - so the fact that your dogs growls means she does not have very good social skills. Sounds like she simply needs to become familiar with other dogs and that leads me back to dog training. She may not need training but the socializing will do her wonders. 

Sounds like she simply needs her social skills sharpened. Dogs sniff butts to say hi like people shake hands but if she is not around other dogs very often she will not know what to do and could become afraid causing her to growl. This is not something you want to continue. Maybe a dog training class would help. She may not need the training but this would put her around other dogs and the trainer could give you ideas on how to correct her problem.

Sounds like your dog needs some socializing. It is natural for dogs to sniff each others butts to identify each other and to say hi. If your dog is not aroung other dogs she may not understand what they are trying to do and this could cause her to become afraid, maybe that is why she is growling, she doesn't know how to respond to another dog. Dog training courses are very good for socializing. She may not need training but getting acquainted with other dogs would be helpful.