Hi Bamboo,
Welcome and hello

I'm sorry for what brings you here -- divorce with BPD involved is really tough. Based on her family history, and her own behaviors, I can see why you suspect BPD.
How can I help her put aside anger and mistrust, while still standing up for myself to some extent?
Her inability to trust is fundamental to her BPD, sadly. You have probably been split black in order for her to preserve a sense of herself in a positive light, an essential move in her mind (though likely not conscious). In other words, you are the last person who can put aside her anger and mistrust at this point.
People with BPD tend to engage in black + white thinking. If she is behaving badly, she has very few psychological resources to process negative emotions, especially ones she is responsible for generating, so she projects this "badness" onto you, where she can deal with it safely from a distance.
It is so emotionally chaotic and out of control for people with BPD, that you have to be the person providing that control and structure. As hard as it may be to see it this way, providing boundaries and firm limits is an act of love. She cannot provide boundaries for her out of control behavior, so to help her, the best thing you can do is be assertive (different than aggressive) and stand firm.
She may not regard the mediator as being enough of an authority figure (same for her lawyer, if her lawyer counsels her to do something she doesn't feel is fair). Often at this stage in divorce, people with BPD are looking for someone they perceive as a "punitive protector," who will take their side and see fit to punish you. A very high-conflict person will even defy the judge, when it comes to that.
I'm so sorry. These divorces are heart breaking, and you care about her and didn't want this to happen. I eventually stopped engaging directly with my ex because I had become such a trigger -- he was stuck in a loop, some kind of script where I was assigned the role of his BPD mother, and any semblance of the man I married was gone.
Don't sabotage yourself if you can avoid it. Like david mentions, write a list of items that are non-negotiable, and if possible, distance yourself from the process. You could be the best negotiator and mediator in the world, the kindest most compassionate and loving person, fair and honorable and good, and yet, you are still a trigger for her and your engagement is likely to cause her to dysregulate even more.
Assertive boundaries are your friend and hers, whether she acknowledges them as such or not.
LnL