Explaining to a Teenager the True Meaning of Christmas

I recently forwarded a poem about how things have twisted away from the true meaning of Christmas. I won't attach it here, but the jist of it was how today's society focuses on the materialism that surrounds the once sacred holiday, how in the name of diversity everything but Christmas seems to be promoted, and the need to be politically correct lest we offend someone who is not Christian. In the end the poem says to stand proud in our faith and wish a Merry Christmas and not hide behind "Happy Holiday" (although this is from Holy Day- I find Seasons Greetings to be a more PC version!). I forwarded this to many people, including my 16 year old little sister. She replied that it was "closed minded" to promote saying "Merry Christmas." I'm not a strong apologetic and don't know how to respond to this. I feel that she has adopted the "worldly" view that adopts human secularism by being constantly PC and taking Jesus out of everything. She is impressionable (as most teenagers are!) and I feel that her words about this are from others. I think this a good opportunity to talk about Christianity with her. However, I need to approach it in a way that will not add more fuel to her fire and will not cause the typical teenage eye-rolling! thank you!