I know what you mean. It really pisses me off when Maggie gets in trouble when one of the small dogs gets aggressive with her. My mom will be like but Maggie is bigger and can hurt them. I try to make her realize that we need to stop the bad behavior not try and stop other dogs from attacking for it(because if we stop the behavior then they won't get attacked).

Grr it makes me angry to, sorry I don't know how to get your sister to realize because I'm trying to make my mom realize herself.

Another thing is the little dogs get away with jumping on people and I'm sorry but when I go to give them food and water and their jumping on me, I get mad, now Maggie gets into the habit of jumping on people too which is awful since she's near 100 lbs. No one is allowed to let the little dogs jump on them anymore because I don't want Maggie thinking it's ok.