I doubt Ariana is totally pure and innocent, but I feel like her "traumatizingly bringing up faith's abusive ex" was her simply reminding Faith that Ralph played mind games and DARVO'd her. That with her own experience, she should be more understanding of her mother's situation and maybe not just blindly trust Daddy-o's narrative just because he's the little Hitler of the house and thinks he can decide what truth is. That claiming the woman is simply crazy is one of the easiest and most common ways to gaslight and turn people against a victim.
It's one thing to take your mom's claim of abuse against your dad with a bit of a grain of salt, but Faith immediately decided she won't believe anything her mom says and will report all possible evidence to her potentially abusive father. No wonder her mom flipped shit. Not a hint of hesitancy against her father nor a shred of loyalty to her mother even with what we already know of how he treats his kids.
Again, not going to assume Ariana is some sweet innocent victim here, but my God Faith, get your head out of your ass. This is your mom, she cannot possibly be worse than your dad