It's in Elaine's personality to be short-tempered and sassy, it's in Guybrush's personality to accept it and apparently like it. ("Generally I appreciate the sass..." -Rise of the Pirate God) I don't really see any abuse here, abuse would be making him feel a certain negative way about himself and as far as I know Elaine has never done that. (not counting when she wasn't herself)
I'm not really sure where people get this master-lackey relationship thing from anyway. I certainly hope it wasn't EMI that planted it.