Well, I think you know the answer to your question.
It sounds as though she was traumatised by her childhood relationship with her parents and with you.
Now - in the present - she reacts to current situations as though it is the past. Partly because she's trying to re-perform the past and somehow change it (that's magical thinking - the past is done; she can't change it) & partly because that's where a lot of her emotional responses to situations were forged (& she hasn't had the opportunity of creating new ones).
It's obviously very sad. I doubt she's very happy.
None of it is your fault, really. You were a child.
She wants something from you (& your parents) that she probably can't have: the past to be put right. At best, she might want demonstrations that she is valued and cared for. But I suspect that whatever you do in the present, it won't be enough because what she really needs to do is accept the past can't be changed, to settle her relationship with it, and move on to how she will build a life of self-worth and value in the present and the future.
It's hard to let the past go if it contained an injustice and a de-valuing of yourself by those who were supposed to be modelling care (& were the people you relied on to give you a sense of your value and worth).
And it's hard to deal with in the present because her responses to incidents in the present will be disproportionate because - really - she's acting out against 'ghosts'. And is probably not receptive to having that brought to her attention.
Because you're enmeshed in all this, you aren't the best places person to deal with this. Plus you're busy. Plus she's probably being utterly unreasonable with you - and why should you now be a singe, tolerating abusive behaviour? It's not your job to give the demonstration of unconditional love she seems to be craving (especially when whatever you do, it won't be enough).
Ultimately, you can only hope time helps bring her self-awareness and resolution. And that better models of relationships help get her to a good place.
You could try consciously raising it with her. She'll explode - but then, she does that anyway.
And you could try just positioning yourself to avoid explosions. And psychologically protect yourself by reminding yourself it's not really about you.
Hope someone else has better advice.