How about chains mounted inside the cab? There sould be enough space between the door and the seat bracket, you could make some sort of small container to keep the chains from slipping out and keeping the door from closing when you don't want them out, so that when they're not in use they're also not dangling to catch on something. Then when she needs them, just pull them out of the container, drop em down- much cheaper hiding step than those stupid $1000 power steps.
Maybe that's what everyone else was getting at when they said chains, but I had pictures in my head of chains attached to the frame rails or something like that and figured there might be a slicker way to do it.