Jpop/Monique wigs tend to run smaller than described. A wig labeled 8/9 will really fit a 8" and maybe even a 7" head, but will stretch to fit a 9". The wonderful thing about Jpop/Monique wigs are that they will fit different head shapes as well as sizes since the cap is so deep!
The odd thing about the Elfdoll's head is that it is more egg-shaped than watermelon-shaped (like I imagine a Luts head would be like).
Kondoll sells some smaller SD sized wigs for wee-noggined kids like Elfdoll, Lati and Dream of Teens!