The Giant Dash comes in quite small sizes - I thought it was a really well specced bike. We fitted one to a customer who is 4'11". She went w/ the most expensive (I think there are 3 in the range) in order to get the lightest possible.

A Bike Friday makes a pretty good (albeit expensive) alternative as it has such a low stepover. I really wish a manufacturer would do a new lightweight & upmarket version of the Raleigh Shopper (ie; small wheels, low step through) as it would be good for my mum too.