Any references to cross-dressing being wrong in the Old Testament refer to Canaanite pagan religious rites. That means they have no relevance to today at all. All reputable theologians express this viewpoint.
So, they are just clothes. Nothing more , and I bet she wears jeans, which are male attire.
Lots of women complain that their husbands hate clothes shopping, so she should count herself lucky that you actually like it. If different clothes liven up your sex life, and you are not involved with anyone but your wife, she should see it as just an extra dimension to you marriage.