boundary help

My dad’s longtime girlfriend has told me over the past years phrases like:

“I have no interest in having a relationship with you.”
“I despise you”
“You are not interesting to me and you never have been.”

There are many more but you get the point.

My dad is aware of such statements and has never asked her to apologize or speak to me differently.

I’ve coached myself through it and tried to open up conversations or gesture of good-will here and there with her, but the situation has continued to escalate in frequency and tone.

After a recent series of events she’s doubled down on such words and actions and I feel 100% certain that it’s time for me to enforce a boundary.

I like my reasons and I don’t want to coach myself to be open to her anymore.

Can you help me identify the boundary?

I’m thinking it might be:

“If you send messages or speak to me using curse words, negativity about me or my family, I will ______”

I could: Send a screenshot right away to my dad so he is aware
I could: block her phone number and/or email address

And the bigger boundary I’m noodling around on:

Enforcing a boundary with my dad:

“If your girlfriend continues this behavior (list behavior), and you continue to condone it or ignore it, I will no longer call, text, or see you in person.”

I’m not saying he needs to break up with her. That is not my goal or even likely to happen. The point of the boundary with him would be that he can no longer sweep things under the rug with me and pretend like it’s not happening. I realize he can’t control her actions – but he can choose to respond differently than apathy, resignation, or denial.