Cinque Terre is wonderful and defiently not to be overlooked. I think you'll be fine with your mother if you have a game plan. Of the towns I would recommend Monterosso, it has the least amount of stairs, and has larger hotels with elevators than the other towns. One problem you may have is with the trains, the stations are small but with lots of stairs, most without elevators. From what I can remeber the Monterosso has the least steps of all the stops about 10 from what I can remember, also there are lots of stairs at La Spezia the station in which you transfer at to get into Cinque Terre. But Monterosso itself is quite flat with only a couple avoidable little hills. I would say you should not have to much problem with Monterosso, but you may with the other towns, I would recommend taking the boat that stops at all the towns as a way to see the other towns without dealing with the stairs. Hope that helps!