I should have built a Shearwater 17 for her, which I'm building for myself right now. The longer boat would be faster too.

It 'ain't necessarily so'......

It depends on the engine room equipment! A shorter/narrower boat with less wetted surface can be 'faster', depending on the paddler strength and average speed desired.

A small light paddler in a 'big' unladen boat (I consider both the Chesapeake and Shearwater in that category) will be blown around by the wind and waves; it can take a lot of energy and corrective strokes to keep the boat moving where you want.

If you can manage it, getting your wife to try some other boats might be useful.

It's hard for me to accept that a popular boat like the Chesapeake has a serious design flaw (cockpit in the wrong place?), but anything is possible, I suppose.