The public transport service of Amsterdam runs a special transport for the elderly and handicapped. It is called Stadsmobiel. It is a van with a wheel-chair access. It works something like a communal taxi. Here is a site where you can read about it: http://www.gvb.nl/english/travellers...adsmobiel.html

If you will be only here for a short time, I do not know what arrangements they make, but I am fairly sure that something can be done for you and your aunt.

Enjoy your stay!