This has been my tactic for a while now, answering with absurdities to reverse the roles. So for instance in this case I'd berate her for implying that TIMs anuses aren't the exact same as vaginas.
I’ve done this but I must be bad at it because they call me terf anyway
You could also reply to her questioning why she doesn't think trans women can't use their feminine penises! After all, they have such a great mouthfeel.
I would reply to her telling her she’s being transphobiquè to imply that “trans women” don’t have “vaginas!” Just to see how much she scrambled to prove she’s not. What about post-ops, Haliey? 😂