Oh great, you got the kurta! Though I don't know what your mom is freaking out about. I used to wear only kurtas to work when I was in the US, and all the non-muslims would really like my clothes. They'd be all - "Oh beautiful, gorgeous, oh what pretty colors!" Lol. And that was in a medium sized city in MN, people there aren't *as* tolerant there as other parts. But they used to think I would dress up too formal and professional - which it was, compared to the sweats and stuff they would wear on "Casual fridays."
You just continue being all "Whatever" whenever you hear any sort of that comment, sis, and you should be fine.