As I understand it the problem your wife has is that that she want to be able to touch the ground when sat on the saddle? That will not be possible unless you have a custom frame built with a much lower BB height - say 9.5in which will also need short cranks - probably 150mm. What she wants to do could then be possible with sloping TT design frame.
But the solution at a reasonable price is to teach her how to get in and out of the saddle when starting up and stopping - almost all shorter legged riders, certainly those riding frames sub 54cm have to learn this if they are to have the saddle at the correct height for pedalling...