Sounds to me like the problem is the frame is too tall for this person. They're saying they lowered the seat so they were a comfortable distance from the ground, but that made their knees come up too high. It sounds to me like the solution would be to get a smaller frame so that they could be a comfortable distance from the ground with the seat height in proper proportion to the pedals. You can adjust seat height on any bike; you can't adjust crank height without changing the frame.