I think there are some details to note here. First, that she was assaulted "early Tuesday morning," meaning after midnight. The Met locks its front (Plaza-facing) doors as the last patrons exit a performance, making it necessary for anyone who might have been in the building (staff, dancers, guests) to exit through the rear. I don't know in which hotel Osipova is staying, but I can't think of a likely one that would have her on Amsterdam Avenue, a residential stretch with no nightlife and, at the moment, a large construction site (badly lit and with lots of shadowy hiding places) -- in other words, a bit desolate, at least in comparison with other central Manhattan areas. It might be a better idea for the Met to keep a security guard on call in the front lobby to allow people to leave the theater more safely at any hour. That way, someone can go out through the Plaza (which is well lit and patrolled, in the easterly direction, directly toward the restaurants, traffic and hotels convenient to Lincoln Center.
Good points, and an excellent solution.