Wow - the advice sure has changed a lot since the days of "put hot sauce on their thumbs," huh? Yikes! Poor kids.
But the truth is that there are a lot of moms whose babies are crazy about pacifiers (that always get lost or dropped in the dirt) that would LOVE their baby to learn to thumb suck. (And as one other person pointed out, there is something completely adorable about it.)
And there is a lot to be said for having a child that is able to soothe herself.
Personally, I'd look for some baby wipes that I could use to keep her hands clean when she's out and about -
mayeb something like "Seventh Generation" that will use safer ingredients - not those hand sanitizers that taste TERRIBLE. (OK, I haven't tasted my fingers after cleaning them with those wipes. Maybe just a warm washcloth with a dab of soap in a ziplock would be better.) Besides, those are harsh to be using all the time, although they do have thier place. They are good for occasional use.
I wouldn't worry about having to break a bad habit, because right now, it's kind of a *good* habit (because of the self-soothing aspect.) Many, if not most children grow out of it on thier own (my little niece announced a few weeks before her 3rd birthday that she was going to stop sucking her thumb when she turned three, and bang! she did it. All on her own. Maybe it was easier for her, since it WAS her decision. Possibly it was her 4th b-day.) Others may need come external pressure, but I think right now the benefits outweigh the downside (the downside being that it *might* be harder to break later on.)
Another option is allowing her to freely "comfort nurse" even if there is no more milk. Maybe not the answer you were hoping for, but having access to... uh... the Real Thing... makes substitutes like pacifiers and thumbs unnecessary.