Zodiac P.I. Vol 3

From the Tokyopop edition

Lill is just like any other normal girl--except she can foretell the future! This "Zodiac P.I." transforms herself into the magic Detective Splca and looks to the stars to guide her way. Before long, she is joined by her childhood friend, Hiromi, who dreams of becoming a detective as skilled as Spica. Soon, no astral investigation is too arduous for this dynamic duo!

Source: Anime News Network Encyclopedia