One of my co-workers plays Dungeons and Dragons and I'm going to add her to the group chat.
Will she be joining your games?
I don't know, the group will vote on that. No one seems to like her, she's not very popular and seems to be a loser.
Even if you think poorly of your co-worker, it isn't right to call her names like loser and assert that no one likes her. Are you adding her to the group chat as a way to make fun of her or pick on her? If so, that's not very nice.
She doesn't treat any of us very well, so why should we have to treat her well?
Even though no one seems to get along with her you should still treat her with respect. Treating her poorly will make her feel quite bad about herself. Invite her to the Dungeons and Dragons game and get to know her, she might just be misunderstood.