I suspect she may have gone through the security via 3rd party car. For example ride on e-hailing car asking for drop off, or friend's car saying to deliver an item, thus security not bother checking who's and what's inside the vehicle other than the driver. Speaking from delivery experiences, almost all of the securities I have been so far won't check one by one who's in the vehicle before letting the car go through the gate temporary for "drop off".

But if I were you I wouldn't make a scene on the securities, more like to the managements. If they don't wanna help your mom then they deserve to get a shouting or two. Or alternatively swap your door lock after confirming the house got no one and she is outside the house.