Empress Flower Garden

Jeongha, our protagonist, died after being hit by a truck on her 25th birthday. Before dying, she meets a strange grandmother who gives her a necklace. Jeongha wakes up in a place that wasn't the hospital, but another world. There she was informed that she will participate in a contest to apply to be the next successor to the throne, where the country is governed only by women and that the next ruler has to choose her emperor/concubine who is a man.