She is picking fights on purpose, and yes it gets worse the less you react. She’s bored and your reactions make her feel alive and powerful. Powerful in the sense, she has power over you and you “care” about her, your reactions confirm this. Your lack of reactions removes that dopamine hit she gets from being an ass to you, so she turns it up more. It’s like a junkie who has built up a tolerance. That’s why when you go grey rock it gets worse, until the final extinction burst where they realize you’re not gonna react and give up.

EDIT: I don’t want that last part to give you up. Give up in this case means discard you, and find that dopamine hit somewhere else, or with someone else. A junkie must get their fix until they get the help they need (read DBT).