She has very small feet and I have large feet.
Is there anything wrong with that?
Different sizes are good for each other
That can be true, depending on what you're doing. But is it really okay to talk about feet like this? It could make some uncomfortable.
Well, I'm also thinking if small and large sizes were a crime, then shoemakers would go out of business.
I think that if it is not bothering you, you should not bring it up. Making comments like this about someone's physical appearance can make them self concious.