Hang tough, in the end your kids are worth the fight. If your W is that hard up for money then she will have trouble mounting a defense. I suspect if you stick to your guns, tell her 50-50 is non-negotiable and you are ready to end mediation and go to court over it, she may very well cave. Even if she doesn't I think that's the inevitable course anyway.
By the way, when she says this:
"She stated she wanted to try to mediate and avoid going to court, and that she wanted me to try to communicate with her openly."
What she means is this:
"This will all go smoothly as long as you agree to all my terms without exception."
She's still a WAS. She's not going to give you any quarter. Load the cannons.
