If there's any room, how about a character who joins the team but is actually looking to mark anything useful or vulnerable for her employer, a merchant or corporation of some kind, to steal and sell? As for her role on the team a mercenary might be the most likely but I'm not sure what would be the most useful given the characters we already have.

EDIT: Actually I'm thinking a sort of stealthy/rogue-archetype character, mainly someone who's good at evading and disarming security systems, with the help of cyborg prosthetics