Would you rather have her or your old boss back? "your old boss" is in reference to the person that is no longer your boss. "back" means to return to the past when that person was your boss.

"In this sentence, what does 'back' mean?" "Back" in this case, means "again" more or less. It's a bit hard to explain, but it's like saying, "Would you rather have your old boss again?"

Thanks for answer