Here's my input:

I. She says you can't wear your kilt because you're not a full-blooded Scot or Irishman. Since she's wearing a qipao, is she full-blooded Chinese, with no other nationalities or ethnic groups in her bloodline, ever, going all the way back to her first pair of ancestors? Not many people are "full-blooded" (that's a strange expression) anyting any more, so that argument doesn't hold water.

II. Since she's wearing a qipao, can we assume that she is wearing it to honor her Asian heritage? If so, then you should be afforded the same privilege.

III. If she's unwilling to compromise on this and "allow" you some freedom on your wedding day, she might not be willing to compromise in other areas. Think very carefully about that before you make any long-term commitments.

IV. Will this wedding be in China? If so, then the kilt will be an eccentricity, and probably look "out of place". Is it to be held in the U.S. or Canada? If so, it might not be such an eccentricity, especially if a few guests are kilted.

V. If all else fails, wear the kilt to the reception and enjoy yourself.

...for what it's worth...