From everything I know there is no law restricting such. Individual companies who hire security, or the security company themselves though, may have their own rules which may include termination if found to be carrying a concealed weapon. Tough it is lawful to do so (carry your ccw weapon) you could lose your job. Perhaps she ought to look at working for Brinks or Loomis, at least they allow open carry of a firearm and won't terminate you for it.