Luna will be a Tribute in the Arena and right now she doesn't really know anything about District 13, but she has medical training and technical knowledge so she can maybe help with investigating/dealing with the trackers or something...if it's possible to do any of that without special equipment, anyway, and without endangering the kids or anyone else involved. Otherwise she values the kids' lives over her own, so she'd do anything to get them out if she knew there was an opportunity.