She explained it later in an interview if memory serves. At the time, she’d just been sexually assaulted irl and Marc plays an abusive predator who kept Bajoran sex slaves in the show, so all her interactions with him were in that mode (he stayed in character between takes) so she didn’t like him at the time. I believe she later invited him over to get to know him better and said he was quite nice in person/out of character.

But she was dealing with a lot IRL at that time (imagine being basically abducted and raped and then carrying on with a 24 ep a season shooting schedule, Nana is tough) and had a hard time with his character. And since that feeling played well into her characters reaction to his character, they just ran with it.

Best I can tell is that they were co workers who had a pretty typical working relationship, and no interest in being friends off set.