Bruss out one curl. Trus tme on this - I've seen a doll ahir salonist do this. DROWN it with water. Then wrap it around a pencil, your finger, anything round. it will dry perfecto. 

Shampoo and/or condition her hair, then use a marker or pen (depending on what size curls you want) to wrap the hair up in a tube on her head. Bobby pin securely. Then, when head is covered in tubes, prepare a pot of boiling water and a big bowl of ice water. Cool boiling H2o for 5 minutes, then dunk her hair  (NOT her scalp )in the water, then into the ice water.  Repeat up to 10 times. Lay her down on a towel and let hair sit for 3 days. Then unwrap curls! (Careful when dunking not to let head or limbs touch the sides;they will melt. Don't get the eyes wet, or they will rust. Finally, don't drop the doll in the water or she will be obliterated.