I have not added to a sister of battle's hair. (strange because I do a lot of sculpting...) However, I have done hair like this. It is fairly easy. Get your Greenstuff ready, roll it flat and about1 millimeter thick. Use your e-xacto blade (with chapstick, water, or some similiar thing to keep the
GS from sticking) and draw it downward in the pattern you want (wavy, straight, etc)
Samples: I do not claim to be an expert...Hope it helps (more pics in my gallery)