Sorry that you are in this situation
@whiteraven - toxic relationships/culture in the workplace can be very difficult to deal with, especially when management/HR are not willing to do anything about it.
I understand your concerns around having a group meeting with her present - I can see how that feels unsafe and stressful.
On the plus side, perhaps this is a sign that her manager and HR are now acknowledging that there is an issue and are taking some steps (facilitating the meeting) to try to address it.
Ideally, for the meeting to move things forward positively (which doesn’t necessarily mean that it’s going to feel like a pleasant, positive experience for you all sitting in there at the time!) you need everyone to participate in an open, honest conversation. So, it may be worth speaking to your other colleagues about that to get a commitment from everyone that they are on board and will speak up. Otherwise, in situations like these, you can sometimes end up with everyone sitting in silence and it then looking like there’s no problem - or only the one person who is speaking has a problem - because people feel too intimidated in the other person’s presence to speak up.
Take it as an opportunity to give her some feedback. To do that really well, keep your observations factual and brief. Be calm, measured and fair in your delivery - keeping things factual will help with this as it keeps things objective rather than people getting caught up emotionally. Don’t get personal. Don’t let things end up with her feeling ganged up on - that will likely end up biting you all on the arse.
Make it clear what the impact of her behaviour is - in you, on the team, on the organisation as a whole....the impacts could be practical things eg around productivity or more interpersonal things eg people feeling nervous around her, or feeling stressed about coming into work.
So, say something like “when you get angry and shout at people, people get upset/feel nervous around you/worry about how you’ll respond, which creates a stressful work environment for the team”. And then you could give a brief, recent example of this happening - so everyone can see you are being measured, not getting personal and sticking to the facts.
Rather than “you’re always so angry, you’re always shouting and screaming - you’re a nightmare to work with and you make us all tread on egg shells all the time!” ? This sounds blamey, judgey and critical so she is likely to just get defensive (which won’t move anything on) and you could end up looking as unpleasant to work with as she is.
I do lots of management coaching, training and facilitation and a phrase that often goes down well is to: go hard on the issue, be gentle with the person. So, focus on the issue (maybe her anger management, maybe her low productivity/frequent disappearances) and then go through (factually and objectively and calmly) the impacts(s) of her behaviour(s)
If she gets angry in the meeting, you and your colleagues need to hold your nerve and stay calm. She will then hopefully shoot herself in the foot by demonstrating what you’ve all been talking about and you will all look like you’re being fair and reasonable and that something needs to change for everyone to be able to work effectively together.
Good luck with the meeting. Definitely try to speak to your colleagues beforehand to ensure that others will contribute to the meeting. And to emphasise the importance of you all being fair, objective and factual so you don’t end up looking like a gang of bullies yourself ? I suspect if she feels “picked on” she will go straight into victim role so you all need to try to not give her ammunition for that.
Also have a think about possible solutions. What would you like to see happen next? What change do you think would help and how can you help support that change? You probably want her to get fired but this meeting probably isn’t the place to say that ?
Hope that helps in some way. Keep us posted?