Hitozuma Keiji wa Moto Mahou Shoujo ~2-juu Spy no Ore ga Sennou Saimin o Kurikaeshi Netori Otosu~

Who knew? Detective Akane Hino used to be Ruby of the "Justice Pirates". Nobody knows about her past life but the other magical girls on that team. Since then she's grown, gotten married, and now upholds justice as a skilled police detective.

However!

An enemy from the past is a double agent spy within the police force and the Syndicate that Akane is currently trying to infiltrate. Akane's magical girl identity is discovered. Revenge comes in the form of a brainwashing hypnosis device the spy gets from a fried food-seller -- a retired mad scientist also from her magical girl heyday. Poetic injustice!

[From DLsite English]