How do I get my 5 month old to stop sucking her fingers?

My daughter has been using her index and middle fingers as a pacifier for about 2 months. She used to use a regular pacifier but didn't really like it. Due to sucking on her fingers she now has blisters on her tongue and cries, but continues to put her fingers in her mouth. Other than putting mittens on her hands or something else to cover them, is there anything else I can do? Thanks!