It sounds like they didn’t ask them to put on a mask. All they asked was for that person to back up which is a perfectly reasonable request. They weren’t being nosey they were asking for personal space. I personally would do the same thing cause I don’t want people to close to me right now. The manager abused his power however for siding with his girlfriend.

You do know how the masks work, right? Me wearing one protects YOU, not ME. So OP had every right to ask someone not wearing a mask to step away from her.

It is her business! If the girl won't wear a mask, she needs to keep her distance. Otherwise, the OP could catch covid from her, or maybe even STDs from the dirty shithead.