Depends on what you want. If you just want her drama removed from your life just put her on "dead to me" and go on with your life.

If you hope that you can mend fences then tell her what you are concerned about. I would not take this step unless you have a pretty good idea that she wants to have a good relationship with you.

You can confront her and tell her what a bitch she is with a list of offenses. But unless she truly wants to make amends this will just be the start of lots of arguements and conflict. She will most likely argue and turn it around to how horrible you are, etc.

My parents always maintained a relationship with my brother's ex wife as did I. But we NEVER compared her to second wife nor did we include her in family events.

I am in exactly the same predicament as you. I am a fly off the handle kinda chic and usually will grab a phone and curse somebody out in an instant.
However, there are those who no matter what you say to them, their behavior will #1 - never change & #2 - will just be overjoyed that they actually got a reaction outta you.
So, I'd leave it alone. That is hard as fuck, believe me, taking the high road while deep down just wanting to slice a bitch is by far the hardest thing anyone can ask of me, but I do it.
Because I ask myself a few questions..."Do I want you in my life?" The answer is NO. "Do you bring ANYTHING of any value to my life?" The answer is NO. "Will telling you how I feel make you change how you treat me?" The answer is NO.
So I just keep it moving.
My DH said it best. "Honey, let BM have my family. You have ME."
Truer words have never been spoken.

I almost always take the high road. We had dinner with fMIL last week. She bought gifts for two fSDs and one for their new baby sister (that BM had with the man she left SO for.)

It felt awesome. Not. I was pissy once I realized this and could not wait to get out of there. Eventually I just left and had a friend pick me up and we went out for the night to see a band play. I know this isn't SO's fault, but it hurts that he won't talk to his mom about what a C U Next Tuesday BM is.

Someone on this site used the word "Enmeshment". That is what happens when two people still have a very personal relationship with each other despite the awkwardness that relationship may cause others who should be *closer* to them.

Personally I think it is up to your DH to confront her on this. Even then, if MIL and BM are friends, neither you nor your DH have the power to say "cease and desist". It is really up to MIL to realize what is important to her.

Bulletproof, one time many, many years ago, BM threw me out of my MILs house.
DH and I were already living together for a few years at this point but were not yet married.
DH and BM were never married.
MIL didn't say boo to her. Didn't defend me, didn't stand up for me, didn't do or say a word.
I was crushed.
Eventually, I drummed up the nerve to call MIL and tell her that what she allowed BM to do was not only wrong it was hugely disrespectful to HER because that was HER home, not BMs.
I told her that I was her sons FDW and that how could she allow such a thing to happen. She was silent. No apology, nothing.
I knew then and there that I would never have a relationship with this woman. She came to our wedding, smiled, played nice. But we haven't seen or spoken to her in 3 years. BM practically lives in her house. We have no relationship with MIL or any of the in laws.