David
Apart from the hard chines, your design looks very similar to my very old surfyak.
That is about the only kayak I have paddled that has even close to the amount of rocker of your design.
I suspect that like my surfyak, it will be easy to turn in its own length. However I suspect that it will want to do that all the time whether your aunt wants it to or not. It will also be fairly slow or more likely very slow.
I would be surprised if the hard chines would compensate enough for the flattish bottom and generous rocker to provide much directional stability.
I believe it is possible to create a design that will be the same weight, will not need a skeg, will be faster and with better tracking while retaining sufficient ability to turn. I realise that you can add a retractable skeg, but that seems like a recognition that the original design doesn't handle the way it needs to.
Perhaps that will be exactly what your aunt wants, but my impression is that she will spend a fair bit of time working hard to keep going straight without making a lot of forward progress.