hmm that is tough. Wonder where she got that idea from.
I'll tell you how I got D there, and maybe there's something in it that might work???
DId the same as you, talked about going while we were at home, talked about what the dentist did, let her look in my mouth yadda yadda.
Made the appointment (for me actually but for her as well). That day I said, mummy has to go to the dentist, would you like to come and see his special chair and him look at mummy's mouth? Cool says D and off we go.
The dentists were great, they gave her a mask and let her kneel up and look in my mouth and have a poke (gently), they showed her how the chair worked, then asked her if she'd like to show them how great her teeth were.
She hopped in that flying chair no issues and opened her mouth....then the two dentists took her on a tour and made her balloon animals she can't wait to go back lol.
We do talk about 'helping' people though - like mummy and daddy are helping people in the community, so 'helping' people are good people IYKWIM? Doctors, ambos, fireies...

Good Luck.
.....I wonder where on earth she got that idea from???
Could she have heard adults talking about it?
Before we mentioned the dentist I made sure I got in DH's ear about not saying anything negative too...