Maven was Selina Kyle's best friend and secretary. She knew about Selina's activities as Catwoman, but, out of loyalty, never said anything about it.
History
Maven worked with Selina for several years and that the two shared a strong bond. When Selina decided to don a costume and stalk the city as Catwoman, Maven assisted her. Specifically, she functioned much as Alfred Pennyworth did for Batman in helping Selina maintain her secret identity and managed the details of her everyday life. She believed Selina's actions to be for the best as they helped animals in need.
Unfortunately, Maven's affiliation with Catwoman got her into trouble with Red Claw, who wanted to contain the security risk that Catwoman represented to her operations. As such, a hired thug attacked her and if it weren't for the timely intervention of Batman, she would have been killed.
Maven continued to serve Catwoman even after she had been taken to jail for her crimes and stood by her during her time in prison and subsequent release and probation. Unfortunately, she had accidentally left a window open allowing Isis, Selina's cat, to escape into the city where she was captured and infected with a virus that Roland Daggett planned to release into the city. After Daggett was foiled, Maven assured Selina that Isis would turn up, which she did.