This Is Screwed Up, but I Was Reincarnated as a GIRL in Another World! (Manga) Vol. 19 - Keyaki Uchiuchi

Ren is a young girl in a primitive world of magic and brutality. Sold as a slave and about to be delivered to an unscrupulous merchant, she suddenly awakens to vivid memories of a past life: a world called Earth, where Ren was both a grown man and a research scientist. Now, she must learn to survive, combining her knowledge of science from her past life with her talent in magic from this life.