I met the most wonderful girl woman a year ago
Fixed it for you 
Honestly, as angry as your ex sounds I see a lot of red flags with your new gf.
Do you try to control her handovers to her ex, and if not done in a matter you deem correct, 'rage' at her? I didn't think so.
However bitter your ex may or may not be, she's right to be furious you are letting your girlfriend dictate handovers.
FWIW, I'm a stepmum as well as a mum. :)
You want this to work, you need to sit down and firmly tell her no more tantrums about your DC's mother. I'm sure for what's best for them if they say 'well mum said...' You suck in a deep breath and don't insult her to your children, no matter what she's said?
Your GF sounds extremely controlling.... FWIW, abuse (emotional/physical/whatever) tends to start when a relationship is at this stage.
Good luck, I hope your talk goes well but please do keep your eyes sharp.