I know that the lines are long, but my friend wants to eat there and can't stand for long periods of time, even with her cane. What can we do?

Grab an open table as soon as you see one and then you go order for them

suggestion: tell the servers that she can't stand for long periods of time , and ask to accommodate her while you wait in line to order. [I mean, there's stools inside the place (with a bar attached to the wall to eat on) and those spots are usually empty.]