Try paying for some lessons for her. It'll make a world of difference.

Without you being present. Get her to bring another girlfriend along. Let
them learn at their own pace from someone that's being paid to do it.

Don't try and teach her yourself. You're too involved emotionally.

Words like "control freak" and "divorce" seem applicable here.

Just how much good is it going to do for your relationship with your wife to
get so utterly freaked out about it? If she's not grasping it, well, what's
that saying? Is it saying she's dumb as a stone? I'm not guessing
discussing it that way is going to lead in productive directions. Or is it
that she just hates your attitude and is deliberately doing a bad job of it?
My guess is somewhere in between the two.

But hey, you picked her, so you're going to have to take a new tack at
dealing with her sailing skills... or suffer the consequences.