I think Holly is actually a sweetie deep down. She just tends to come off as a bit "ditzy" every now and then. I've known people like that. The irony is that I do think, when it comes to social intelligence, Holly is actually smarter than Debbie in that department. Maybe she doesn't always come off as down-to-Earth, but she would at least know better than to intrude on someone's personal space like that, or say something rude or mean on purpose. And keep in mind, Debbie was the one who pointed out Emily was gaining weight to her face, and Holly reminded her not to do that. Or maybe Holly just doesn't like awkward situations or potentially getting caught up in the middle of conflict, so she tries to defuse them with silly jokes (hence "you and Maria are exchanging hairstyles!").