My pops lives part of the year in Los Boliches which isn't far from Benalmadena. IMO Los Boliches is a fab place to stay and very flat which would be perfect for your Mum. I went to Benalmadena not long after the marina opened and it was really nice and as long as your Mum doesn't want to walk far then also good for her. Plenty of organised trips to get around,also a brilliant and easy to use train system running along the coast!