I fully understand what you are experiencing.
My wife and I are often the best dressed at a restaurant or other function which goes noticed by others who are there. Often it is the other women that make it miserable for my wife; sly comments in the bathroom, scowls and sideways glances, all for just being dressed better than they are. Or even worse, nasty comments from her own family, “your heels are too high”, or “your skirt is too short”. Yes I can commiserate with you on what you are saying. I deal with it by doing my best to be understanding. Since we like dressing up and looking our best whether it is at church, a restaurant, or a show; we do, and ignore the comments, even if it is not easy sometimes. While others might feel we are dressing up and thus making them look dressed down, that isn’t the case. We just like looking sharp individually, and as a couple.
1. I try and encourage my wife to dress up by dressing up myself. If she sees me looking sharp, she tends to follow suit in matching me. However, if she chooses to dress down, I still dress sharp. I don’t berate her or beg her to wear something better, it is her decision on what she wears, but by staying true to looking sharp myself, it just shows her that I will stay the course.
2. I understand that high heels are not comfortable and have a back up pair of shoes for my wife like ballet flats. As much as I love her wearing heels, it is better to have her start in them, and have to take them off mid-date through, then have her resent wearing them at all. I always have a more comfortable pair of shoes on me, or close by in the car, etc.
3. Take them to venues where it is more typical to be dressed up. Nice restaurants. Upscale performances. Live Theater, etc. By not standing out, they will feel more at ease dressed up, and thus wearing high heels.
3. A lady needs three things: food water and compliments. A wife can pick fake compliments out as soon as they are uttered or texted, but by being honest and telling them often how much you appreciate them wearing high heels, and how good she looks in them and other honest compliments, she is more inclined to wear them for you.
4. Like all interests, be wary of falling into the trap of making her feel as if you just love her because she wears high heels, or you just love her when she has high heels on. A woman wants to be truly loved, and while they like dressing to please the man she is in love with, she does not want to be reduced down to being loved just for what she wears. Or feels she has to wear high heels to be appreciated. It is a very fine line I know, but this is why several other suggestions I offered above come into play.
In closing, just understand that a woman has some six hundred images per day they are subjected to on what the world thinks the ideal woman looks like. Naturally most women do not feel they measure up. As husbands and fathers we are battling the world, but we cannot give up and let our wives, girlfriends and daughters know we are proud of them whether sharply dressed or slumming for the day. We ultimately have more sway than the world, but we must be understanding. Maybe these suggestions will resonate and work for you.