Is she drinking so much water that her urine is clear? If so, she's drinking too much. I've read that, paradoxically, drinking excessive amounts of water can cause some of the same symptoms seen in dehydration.
If that's not the issue, then I'd suggest some of the Burt's Bees products:
/www.burtsbees.com/shop/lip-care/lip-treatment/www.burtsbees.com/shop/lip-care/lip-balm (the plain Beeswax lip balm works great for me)
Good luck!