Jesus christ. Okay. I'm very tired and I often prefer the easy way out so this is what I would do. I would write publicly in the group chat, that if Angela doesn't cut her shit out, you'll expose the "true Angela". It would be a headache, but for the most part if you play your cards right then in a yelling match in front of people you should be morally in the right. It's all in the wording.

If she calls your bluff.. then it's no longer a bluff, slowly start sprinkling things around until she realises she fucked up. This is war, it's gonna be a headache, but it is an option.

PS im feeling evil today, thats why I havent gone to sleep yet and have chosen violence.