The Girl is Murder Series by Kathryn Miller Haines

Iris Anderson is only 15, but she's quickly mastering the art of deception in this YA novel for fans of Veronica Mars.   It's the Fall of 1942 and Iris's world is rapidly changing. Her Pop is back from the war with a missing leg, limiting his ability to do the physically grueling part of his detective work. Iris is dying to help, especially when she discovers that one of Pop's cases involves a boy at her school... moreIris Anderson is only 15, but she's quickly mastering the art of deception in this YA novel for fans of Veronica Mars.   It's the Fall of 1942 and Iris's world is rapidly changing. Her Pop is back from the war with a missing leg, limiting his ability to do the physically grueling part of his detective work. Iris is dying to help, especially when she discovers that one of Pop's cases involves a boy at her school. Now, instead of sitting at home watching Deanna Durbin movies, Iris is sneaking out of the house, double crossing her friends, and dancing at the Savoy till all hours of the night. There's certainly never a dull moment in the private eye business. less

Iris Anderson and her father have finally come to an understanding. Iris is allowed to help out at her Pop's detective agency as long as she follows his rules and learns from his technique. But when Iris uncovers details about her mother's supposed suicide, suddenly Iris is thrown headfirst into her most intense and personal case yet.