it might not match her MacGregor scarf because there are a bunch of different MacGregor tartans all of which are genuine. there are hunting, dance, weathered, modern, ancient ect. the tartan sport kilt uses appears to be one of the modern hunting variations. hers is probably one of the others. the reason i bring this up is it is another avenue for you to discuss the kilt with her, it's historical implications and its relevance as an acceptable garment, ect. the more you educate people the less they have to be prejudiced about. plus if she knows it is a genuine MacGregor tartan she might be more accepting. here's a link to a bunch of MacGregor tartans:
http://kiltstore.net/sr_swhdr_eighty...Gregor:stage=2
good luck. like anything acceptance usually takes time.