Gaslighting daughter with ADHD/ODD

Hi,
My 18 year old daughter is a brilliant gaslighter and often runs circles around me.
For example, we had this dialogue 3 days ago:
Her: can you pay for my surgical procedure? (It’s a non-urgent procedure but it does need to be done)
Me: I can help you with it but not right now… (I’m a solo mom)
Her: Are we broke? Why can’t you afford it
Me: I’m still paying off your school fees and have paid thousands over the past two years so I don’t have extra money at the moment
Her: (angry,shouting) oh you’re making me feel bad! I don’t want your money!
Me: okay.

Yesterday…
Her: So can I have that money now for the procedure?
Me: do you remember the conversation we had the other day?
Her; Yes, you said you’d pay for it!
Me: do you remember You said “you’re making me feel bad! I don’t want your money” – do you remember that?
Her: I never said that! youre just trying to get out of paying for it! Even if I did say it, you should have checked with me…

I think as a mother I should help her and pay for it (she is working two jobs and can afford it though), but I also want her to take responsibility for saying things in anger and then conveniently forgetting them…

How do you think I should handle this situation?

Thank you 🙏