HI,
I think, you need to work on distracting her whenever she puts her fingers in her mouth. Since she has turned two you have to start immediately working on this lest this habit stays for long.
Make her sit and tell her that if she will suck her finger, her teeth will come out like an elephant. I mean tell her whatever scares her a little in putting the finger in mouth. This only will not help her quit the habit but she will atleast decide to leave it. Overtime she will put her finger in mouth she may remember what it can do to her and she may stop doing it further.
Parse her whenever she is not sucking her fingers. Appreciate her a lot and appreciate her infant of others for leaving the habit. This will make her feel good and she will work on it more. Reward her when she doesn't suck the fingers. See what are the timings or situations when she sucks on her fingers, during those times, find the ways to distract her. Give her clay dough to play, give colours to do or make her play or read. Practice positive reinforcement. Praise the baby even if she tries once in the whole day to avoid sucking. Your continuous involvement, rear will help her shun the habit for sure.
http://www.colgate.com/en/us/oc/oral-health/life-stages/childrens-oral-care/article/ada-11-tips-to-break-thumb-suckers
http://www.mayoclinic.org/healthy-lifestyle/childrens-health/in-depth/thumb-sucking/art-20047038
Chetna Joshi