I once gave tourists directions to the wrong train probably took em about 30 minutes to realise something was wrong *cringes hard*

Just call security on her for attempting to break through the gate...LOL :)

You're human. Things happen, and just say that you forgot that the gate is locked, and that you hope that her trip to the security office and jail weren't too bad as you were duty-bound to call security when she attempted to get through that way, once you realized it was locked, even though you instructed her to go that way. :)

I do apologize if I make a mistake, and I will take extra care when giving directions, such as to someone driving with bad cell reception who cannot find a landmark. I even give them directions that may be longer, and I tell them this, but with fewer turns, or more readily identified intersections/turns.