J.S.
I think everyone has a different perspective on this. I was quite happy to have my son suck his thumb because it was always with him, couldn't fall out, etc. From my perspective it was much easier to deal with than a pacifier.
Thumbsucking is about self-pacifying. Think of it this way...if it helps your baby sleep, be calm, etc. rejoice!
And they grow out of it when they are ready - my son didn't suck his thumb in public and stopped on his own completely when he started preschool.
Just like anything else, when the time comes it will be easy to establish rules on where sucking her thumb is appropriate, etc. In our world, blankie doesn't leave the house unless we are going overnight someplace. As your child gets older (over 2, etc) just establish that she can't suck her thumb unless she's at home, and then in her room, and then in her bed.
In the scheme of things, this falls into the little things category for me.