When you are calm and feel closer can you talk to her about how you are going to react when she is angry, and what you will tolerate when she is angry?
DS has been like this and it has taken time but I sort of had phrases that I repeated which he knew I had a 'rules', and in having an agreement over them, I felt more in control of how I dealt with the situation.
He knew he should not hurt his sister or be verbally aggressive to her.
Nothing should get damaged. Smashed. Thrown.
He could not swear at me.
I would Try to calmly state that 'we' need to calm down before we can resolve anything.
I would use 'we' as it is less accusatory and stopped me from 'over' punishing him whilst still angry. (you can't actually ground then until they are 34, or NEVER give them pocket money again
)
I told him regularly that I believed in him and that we would get through it, he has a lot of potential and that I understood how hard it was.
He thought he was 'bad' and couldn't change. So he would actually behave worse.
I taught myself to wait for an apology when he had calmed down instead of shrieking for demanding one in the middle of a row. It would always mean more when he had calmed down and I achieved nothing by adding wanting an apology in the middle of the heat of the moment.
We always talk after just to iron out what caused it, why I felt the way I did and why he felt the way HE did.
Things changed quite a lot for us when I told him that I loved him unconditionally, but that that wasn't a license to behave badly in order to test that love.
I told him I was his brick wall, and there were boundaries he wasn't allowed to cross, and that however much he hated that now, I would be doing him no favours in the long run by just standing by an letting him behave badly.
Punishments were on two levels. Something to balance what he had done, and something that he could actually 'earn' back with better behaviour.
Even if it was confiscating his X Box for two days, and the first day was fixed but if he did something that showed he was truly sorry, then he could get it back earlier. This gave him an incentive to improve.
Sorry for the essay, but we have been truly to hell and that we are in the place we are in now is amazing and if anything we tried helps, I would be glad.
DS also talked to someone, which helped a lot. However much I love him, sometimes I think hearing stuff from 'mum' just made him shut off.
All the best x