1.) Find somewhere for her to sit down;

2.) Queue for taxi;

3.) Ask cab driver to wait until you retrieve mother;

4.) Retrieve mother;

Alternatively exit the station by the openning on the east side, near
platform 0 and 1, on York Way. This is where taxis set down for the
sation. You could ask a cab driver here to take you wherever it is you
need to go. I'm fairly certain he would not mind, and that you would
not have to queue or even wait long.

Of course if every one did this it would be fairly chaotic, and should
be generally discouraged, but it would be excusable for your 85 year
old mother.

Lorenzo.