Baby mama issues

Before y'all get all pissed off thinking this post is about bashing my SO's baby mama let me tell you I'm not into that. 
(Oh and it's a kinda long rent. Sorry)
So ever since baby mama found out about our engagement she started harassing me and my friends and including my dad on Facwbook. 
She would go on my posts and make nasty comments and send me nasty messages. 
I never replied, I just blocked her and carried on. 
Not happy she proceeded to harress my friends and even my father. She would make comments on my brothers in law's facebooks saying my SO was dating some dirty Brillo hair bitch (picture of my "Brilo" natural hair bellow👇🏿👇🏿👇🏿, funny part is that she's a Black Dominican much darker then me. Lol)
She also got her girlfriends to go into my SO's Facebook make nasty remarks about us. 
He also ignored them. 
Not succeeding in social media she then started saying things to his family (it's a big family and not everyone knows the details).
She started telling his cousins and aunts that he was getting involved with a Brazilian gold digger and I was just marrying him for a green card (funny thing is that I've lived in 5 different countries including Dominical Republic and US and visited several other before and never had a problem with immigration) 
Why all the Facebook talk?
Here is: The deal is I'm Brazilian and my parents were missionaries so we always travelled a lot and in one of these travels we ended up in the US where I met my SO and we dated in high school when I was 16 and he was 18. 
(Long story short he was deployed to Iraq my family and I went back to Brazil and we lost contact for almost 10 years. I got married and had a baby got divorced he knocked up his college fuck buddy)
Ps: they didn't date, it was casual sex. Silly boy didn't put on a Jimmy cap cause his fuck buddy said she was on pills (now who the hell fucks casually without protection? Thankfully there were no STDs involved). 
She also showed my mother in law an article about a man who's daughter was raped by his step son (my son was 7 at the time). 
She told my mother in law and my significant other that my son should never be around her daughter because of that. 
So 2 years ago I came back to US and we got married. 
Met the baby mama and treated her with respect. 
I was determined to make things right between us all. 
My step daughter loves me since the time we used to talk on Skype when my SO had her around.
On my first thanksgiving with the family she set on my lab through out the whole dinner and ate off my plate. (It was a little uncomfortable because my kid for jealous and baby mama was super bothered but played cool for the family) 
When she met me she was really exited, she's an adorable child regardless of some behavior issues like trying to kiss my son and even trying to expose her private parts to him and hitting him with a stick on the face cutting his eyebrow open, and putting a pillow over my 4 months old baby while she was sleeping. 
(I never blamed her for any of that, her mom is the problem. She brushed all of those problems off when I talked to her about it) 
So for the past 2 years I've been trying to be "the greater person", the problem is she's not only been taking advantage of me and still saying shit about me to the family. 
I have never said anything to her or even engaged in conversations about her to my mother in law or any other family member. 
Two years passed and I just feel really stupid for being so nice to her. 
Even my personal therapist says I'm too nice to her and letting her take advantage of me. 
We even have a family therapist who told my mother in law my SO and his baby mama have to stop relying on me so much because it's overwhelming and unfair.
I feel really frustrated at how some women can be real bitches even to other women who did nothing against them. 
It's sad and not of my personal nature but I have decided I'm done being nice to her. 
The shit part is that I really don't know how, since I feel like being mean to the baby mama might affect my step daughter. 
But unfortunately all of this has been really taking a toll on me. 
I've even been put on medication for anxiety and had to give up breastfeeding/pumping because of the meds.