finger sucking and nail biting

[janeinbarcelona]

My 3 year old daughter has sucked 2 fingers and put a third finger up a nostril for as long as I can remember. She doesn't only do it when she is tired, but throughout the whole day. And I don't think it is related to boredom as she does it while she is playing as well. I kept thinking she would grow out of it but there are no signs of her stopping. I don't want to stop the comfort she obviously gets from it (it would be ok if she did it to fall asleep for example) but she is getting hard skin on her fingers which I'm afraid will only get worse with time. Does anyone have any suggestions?
In the past month she has also started biting her nails. I thought about using the horrible tasting stuff for the nails but wondered if she is too young. Any advice appreciated.