Help please to stop finger-sucking

[YBR]

My DD (3yo) never took a dummy but found her fingers very young and still sucks them at night, when tired or stressed or upset.
I'm noticing that her skin is sometimes raw or blistered from it and I'm sure it can't be doing her teeth much good. I need some foolproof ways to stop it (without causing harm)!

At the moment I've been focusing on daytime by repeatedly telling her and taking her fingers out but she is resistant, defiant even. I've thought about covering her fingers in something foul-tasting but I'm not sure what (and I'm not ready to be that cruel yet).

Has anyone any advice/experience they can share please?

My son did this. He stopped literally overnight by himself at about 3.5. They had a talk at playgroup about germs, germs being on everything all around us and washing hands or germs end up in your tummy. Not sure what he took from the talk but he said "he did want germs in his tummy so he wasn't sucking his fingers" His playgroup teachers were lovely so they weren't meaning it in a scary way. Maybe a chat along those lines......

And he had done it from about 3 months old.

We're in exactly the same situation. 3 year old sucks his middle 2 fingers and he has hard bits from where his teeth sit. They stink in the morning too.
I'm constantly telling him to take them out in the day. Will try the term chat