Some modifications ahead.

[mishawakaskirt]

I just ordered two woolen kilted skirts from eBay from across the pond. International shipping sucks. I know it will be less than perfect, the 40 inch long one is for my wife, it will need the straps lengthened two sizes. She has always wanted a long tartan skirt. Won't she be surprised. The second, blue one is for me, I love that color of blue. If it fits perfectly, I may do nothing to it. If lest then perfect. It will need to be shortened, fell added And I may attempt to Right hand it into a proper kilt.

[mishawakaskirt]

Forgot to add the pictures.
Here you go.

s-l400.jpg

[r.m.anderson]

Consider taking the straps off of your left sided kilt and using them on her kilt.
With your kilt now being strapless think about the using Velcro as a method to close the waist.
Familiar with SportKilt kilts and the Velcro closing ? - Velcro is used between the two aprons
and it should be very easy to make the left sided kilt into as you note a proper right side kilt.

So you don't need to purchase straps for hers and you only need about 8 inches of Velcro on yours.
Sewing is the only other expense labor involved.

Nice blue colored tartan on yours - I like it !
If it were my project would shorten it to the 2nd red line from the bottom - something around 19 inches hem.