I call it a twist braid (i'm not sure what it's actually called)
first you split your doll's hair into two sections
Then take one section and twist it toward the left.
Twist the other section toward the left also.
Then cross the right section over the left section or you can cross the left section over the right section. It really doesn't matter which :) And twist them toward the left the whole time.
twist it down as far as you can.
And there you go :)
Hope you enjoyed!
Let me know if it works out for you.