Hello Dominoe!
Getting a taxi to the Superdome during a non-special event like the Sugar Bowl, Super Bowl, etc....shouldn't be all that difficult.
I suggest that you have the taxi driver take you to the POYDRAS Street (GATE A) Entrance at ground level. There's a huge pedestrian ramp that goes from the main entrance level to ground level. Go underneath that ramp.
There's also plenty of information at www.superdome.com the staff at the Superdome are very accustomed to accommodating special needs. You won't have a problem if you arrive at least 1 hour before the event if it's a Saints game or something like that.
I hope you enjoy your visit to New Orleans.
-Gene