The thing is, you are letting her abuse you! You need to walk away and stop engaging! You are letting her attack you emotionally. You see a text that doesn't pertain to S3, don't read it. DO NOT spend time together, do not let her in, hang up the phone on her when she becomes like this.
Quite putting yourself in this position. You have control over this. She can't use a tactic to make you feel guilty if you don't listen, cut her off, walk away!
You have full custody, don't you? So, don't let him go there if you feel it is unsafe with the pitbull. You have that power, exercise it. She can't just take him out of a daycare and put him in another if you don't agree and you contribute.
If you have full custody, she can't make these decisions without you. She is threatening you and you are taking the bait.
exercise the power you do have.
She's as abusive as much as you let her abuse you. Stop being a victim and do take some control.