She will need some pretty clear boundaries - no riding in cars with boys etc.

She will also need some tools to help her deal with her anger (or whatever it may be) when it surfaces again. Maybe it's ok if she storms out of the house - but can she agree to go for a run around the block to shake it off etc.
If she doesn't feel like talking things out, it might be ok for her to hibernate in her room with a 'do not disturb' sign - or even (my fave) stick a certain colour post it on the door to signal "bugger off", "feeling sad" or "I might want to talk about things later".

If she and your mum can come up with a plan that A feels might work when she wants to blow up, she may be able to slow it down or stop it altogether. But mum must remain in control - with A's input. And it might take a bit of time

My little one goes off like a rocker and has said several times that "he doesn't want to be like this", so when I can feel something brewing I have had success with saying to him "remember, this is not how you want it to be -what can we do". He often falls into my arms crying with relief that he doesn't have to maintain the rage.

xoxoxo

GL!