Garden of the Dead Flowers is a Manga/Manhwa/Manhua in english language, Webtoon series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

When Mila woke up, she suddenly returns to the past in Batavia during the Dutch colonial period. She accidentally saw her grandfather at a young age, kill a girl! Her grandfather, who she thought was nice, actually killed girls in his garden and planted them into flowers.