All you need to do is make sure the ground staff in LCA log her in the system as a WCHS (wheelchair stagger) this code means that she cannot use steps and a high lift vehicle will automatically meet the aircraft.
Your mother will be taken off the aircraft and they will tell you where she will be dropped off so that you can meet her, she will be then taken in a wheelchair with you to arrivals.
Nothing to worry about at all as this is a normal procedure.