Bite her finger slightly every time she does it, this will hopefully make her realise that it’s not really comforting for her. By slightly I mean literally pressing your teeth slightly against her fingers so she doesn’t find it comforting 🙃
Did you let her to begin with or is it an on going no situation?
Just go cold turkey. It's your body, your choice. Redirect "I don't like your fingers in my mouth. You can hold my hand". She will meltdown for a few days but stay consistent. She will adapt.
Awww bless her 😂. My younger sister used to play with our ears to fall asleep. The other one had to turn her head left and right non stop to sleep. Now my daughter has an obsession with the corners of the pillow. So weird she has to have a pillow to put on her whole body, she plays with the corners and has to bear hug it 😂. I just let it be if that’s what she finds comfort in sleeping and it’s not dangerous I just let her carry on and not worry about it. One day she will outgrow it x