At the moment I am using a mixture of oils.
I think the best ones (in my case) are peppermint, Amla, Brhami and castor. But thats in my case (I use more oils, but I think those are the ones that areworking for that problem)
Why is it that you think her edges are bad?
Do you moisturise them regularly?
Tight braids? Tight Pony tails?
Is she getting enough Iron?
These can all be problems.
I had to evaluate these aspects... I know I am aneamic (low iron levels in my blood) which is bad for the red blood cells (that contain iron) to carry the oxygen around my body (especially my hands and edges!)
Up her leafy greens intake, or find a childrens multivitamin that contains Iron and Vit C (you need the vit C to absorb the iron)
Stop giving her tight hairstyles if that is a problem