NEED HELP! Aggressive behavior

Needing immediate advice.

I have one dog, a newly spayed husky mix female, that is randomly super aggressive to just one particular dog in our house. We have three. One bigger than her that she never ever bothers and one smaller. She will attack the smaller one, again, randomly, for no reason. Today they were just playing in the yard, he walked by her and she was on him. Punctured his head (not terribly bad) and busted his ear which bled like a stuck pig. I am at a loss. I don't know what else to do to stop this. If there was something he was doing that upset her I could stop that behavior but there is literally nothing that he does in particular to correct. Note that I live in a rural area, live an hour from any major city so driving an hour each way several days a week for any kind of behaviorial training is just not doable right now. Any and all help appreciated.