What Causes Lack Of Pubic Hair Even Though Puberty Has Started?

Our daughter is adopted from China. She is a petite 12 year old. She has developed breasts and hips. She has been irritable lately. She does not have pubic hair, but got her first period two days ago. Is there a problem that we should be aware of because she does not have pubic hair? Someone had mentioned that this could be normal in young asian girls.