Chad is right about growling is just a way of communicating. We have 3 greyhounds and each one tolerates behaviour of other dogs differently.
Brooke is the most tolerant, so when she growls I know the dog's behaviour is really really obnoxious and I may mention this to the owner, depending on the situation. Ben will tolerate a lot but not a dog who lunges at him or tries to mount him. Ben will growl so I rarely have to step in. Katie is the least tolerant of bad dog behaviour and since I know this, I will allow dogs to sniff her if they greet her on her side, but I will step in between her and a badly behaved dog so the dog can't get near her.
Without knowing all the details, your greyhound may be less tolerant of badly behaved dogs and is letting them know, rather than being cranky. She did fine with the last situation you mentioned. I suggest you read a good book about dog social behaviour and see if you can recognize the signs to see which dog is causing the issues you describe.