Hi RJ, a couple suggestions for skin softeners that are 1. edible and 2. child safe. My first recommendation is jojoba oil. You can find this at any healthfood store. I use it myself and on both my boys (3 & 18mos). Easier on the budget is any food grade oil - olive is nice. Try massaging it in lightly after soaking the hand in warm water. Maybe even putting socks on after for 15 minutes or so to help it absorb into her skin instead of her mouth. Oil does get everywhere. Honey is a wonderful moisturizer, but not appropriate for any child under 2(?) I think.
You have two different issues here. One is the thumb sucking, and the other is the skin. I personally sucked my thumb until I was eleven. And I have chronic eczema. My sons have inherited my skin and we're working on weaning the oldest from his pacifier. When you're all ready, I would strongly recommend weaning her from the thumb. It is so hard, but ultimately worth it. If it takes 21 days to make a habit, then it can take 21 days to break the same habit. My pediatric orthopedist had my parents buy a bottle of "thumb." It tastes awful! For week 1: apply 'thumb', a band-aid and a sock over the hand. Week 2: just the band-aid and 'thumb'. Week 3: just 'thumb.' I'll get off my soap-box now.
CRose