Pickle, IMO your Ws choice to begin to wear heels over flats is less a sign of disrespect and more a conscious decision to do something to make herself feel more attractive. I am not saying she did not think about how much taller she would be and how that might make you feel, but I think this was probably a momentary thought.
When I was younger, I wanted my date to always be taller than me. I wasn't extremely tall, but I was a little self conscious about it. When I M my H, he was about two & 1/2 inches taller and I didn't wear heels that put me taller than him, but it had nothing to do with "respect". I never even considered it being a sign of disrespect if I was dressing to be taller. It didn't bother him.....it was me and my insecurities. As the years passed it didn't seem to matter if I was as tall or taller than my H, and I wore whatever I wanted.
Wearing high-heels might be part of your W's rebellion playing out, IDK. But I would say that it is more about "her" and the look she wants. Let's face it, flats are not very attractive when a woman is trying to look dressed up. And if she wants to look sexy, she better have some heels on. (Besides, we women feel younger.) I can tell you that wearing flats does not give me the same "feeling" as wearing high-heels. So, I think that she just reached a point of...."Forget him, I'm dressing up in a pair of real high-heels!" At her age, why not? She's wore flats all these years just b/c of not bruising your ego? Come on, Pickle.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!