Entitled coworker was not invited to a coworker's birthday party and thinks she gets to be an asshole all day

I work in a small office, five of us and the boss. We all work from home. One coworker is a real toxic asshole. She is mean, rude, condescending and an all around unpleasant person.

One coworker had her 30th birthday party yesterday. It was one of those painting places where everyone watches the instructor and paints. I had no idea she wasn't invited until this morning.

She was like a pit viper all morning, being mean, rude and insulting, showing everyone mistakes they made months ago, taking personal digs at each of us, called the birthday celebrant fat (entitled one is 300 pounds and 5'5 lol) and yelled at me for not answering the phone fast enough.

She finally asked me why so and so didn't invite her to her party. I told her to ask her, but if she's pissed she wasn't invited, she doesn't get to treat everyone horribly all day.

She finally confronted the birthday girl who told her

"You're mean and hard to be around, and I don't like you. That's why."

She's been silent since then, thankfully.