A separate lawyer I talked with on my own says that mediation seldom works with someone with a personality disorder.
In general, that is true. But you can also look at mediation as part of a longer term strategy.
In my case, we settled 98% of everything in mediation. I would not agree to joint legal custody. So our order was exactly that: finances, house, cars, retirement, even physical custody and visitation. Plus one item mentioning that we did not agree about joint legal and it was a matter to go before the court.
My ex is very narcissistic, though. I think that motivated him to appear reasonable, and be the big man on campus. He's the kind of guy who buys everyone's dinner even if he has no money.
So I expect we'll soon hire our own lawyers, and that expense makes me even more reluctant to split fifty-fifty. I am thinking that to protect myself I will have to adhere to the letter of the law; but to take care of the woman I still love, send her monthly gifts to make it even.
Treat divorce like a business transaction. A legal separation may or may not be best. My experience is that people with PDs will fight even the things that benefit them, just because you suggest it and want it. So yes, ask for as much as possible so that you have money to enforce the things she does agree to. Getting a settlement taken care of is only half the battle <sigh>. As much as you can, keep the highest legal upper hand so you can mete out fairness on your terms.
An example: My entire alimony check goes toward legal bills each month. I pay my lawyer to file motions for contempt of court for things that N/BPDx agreed to in the original consent order. It's entirely silly, especially now that N/BPDx has been ordered to pay my legal bills.
She demands that I pay the rent there out of my own money, not common funds, while we continue to split the cost of the house as long as she wants to live there. She even demands to be paid for keeping it up, for a couple of vacations, and maybe for a new car.
I don't have much of a soft spot for pwBPD anymore, but I do think that the person being divorced tends to take a longer time understanding the implications than the person who filed for divorce. My advice is to have businesslike boundaries as soon as possible so you don't feed into the typical fantasies of reconciliation that your wife may harbor. If you're done, be done.
Follow the law and do what your L recommends. If you're like a lot of us here, your divorce is going to cost a lot of money. High-conflict divorces are high expense. Get a good L who has a good strategy and go from there.