Thumb sucking

I have a 4 month old baby girl. Her doctor, from the very beginning has always told me to not let her suck her thumb but pacifiers are ok since you can take them away. Well my baby has been sucking her thumb for about a month now. It helps her fall asleep and stay asleep through the night, which is nice. She does not like pacifiers. I have tried the nuk and soothie kinds but she just doesn’t like them. She’ll take them eventually but she REALLY fights it so I don’t really bother with them. She has an appointment coming up on Wednesday I’m kind of nervous for because I feel like her doctor is going to say something. What do I do if he does? Also how do I get her to stop when the time comes? I don’t want her sucking her thumb once she gets teeth.