But someone on another board here posted a link to this site:
The owner has a mix of hair textures that sounds similar to your DD's. Her hair is very very long and she wears it out all the time, and you can see from her detailed pics that it's moisturized and healthy all the way to the ends. She goes into great detail about technique and particular brands of conditioners she recommends (mostly cheap and readily available). She also separates out the curls when they're wet so each curl holds its shape--and that really caught my eye as something that might work to have the curl protect itself and not poof out or get dry at the ends.
Anyway, I want to try this on my DD's hair soon, and when I read your post I thought it might work for your DD.