This hairstyle is called "Saeang-meori" or "Saeng-meori" (Meori means the hair). It is the formal style for girldom. Unmarried women just braided their hair normally, but they made the hair like this when they enter the palace (for full dress). And this was also the hairstyle for some young court ladies, but not everyone. Just for high level maids. For example, in fact, Dae Jang Geum coudn't make her hair like this because royal kitchen ladies were in low level position.