My mum tried everything to get me to stop sucking my thumb - I still do it now at 27
I remember being a kid and having cracked bleeding chapped thumbs due to the wet/cold air getting at them. Was really painful but my love of my thumb won
Things mum tried were... plasters (I peeled them off), plastic finger wound covers taped on (again I removed them), gloves (whipped them off), that nail stuff stop and grow that tastes revolting, prob best not to use n broken skin- just a tiny bit on nail, It didnt work for me as I learnt to suck really fast & spit repeatedly until the taste had gone
Um she tried to shame me with dummys at about the age of 6 but I loved it so my granda had to 'accidently stand on it and break it', she also tried bribary as I got older eg dont suck your thumb today and you will get xyz, and constantly batting it out of my mouth.....
Basically my mum tried everything! I refused a dummy from birth and have sucked my thumb ever since. Try a few of the things Iv mentioned but tbh dont beat yourself up if she carrys on. Its horrible having sore thumbs, and they may get infected but the problem is you cant cut them off and it really depends how determined hollie is. x