Aggressive only to Submissive dogs

Question
Our 1.5 year old Female Spayed Yellow Lab is a big goofball and generally great with other dogs. Unless, the dog shows submissive behaviour. Including with dogs she has known since she was a puppy. All is fine until another dog shows to be submissive, then she will get very aggressive ( read: scary) with them. If dogs are not submissive, she's happy to play wrestle relatively gently. Any help ?

Answer
Did you get her as a pup or as a rescue?  It sounds like she has some issues with socialization.  Knows her place as a submissive, but doesn't know proper behavior around those more submissive.

Have you taken her through obedience training that allows time for socialization?