Rejecting the Sunnat of Nikaah

There's a thing that is bothering me so much. A friend of mine hates marriage. Once there was a chart in my college that listed the sunnahs of Ambiya, one of them was nikah. She didn't believe that it was a sunnah, we told her that it was. Afterwards she jokingly said that she will cut this off the chart. Is this kufr? If this is indeed kufr and takes her out of the fold of Islam, she is going to be super offended and likely to throw a tantrum because nowadays people don't even know things that are kufr. How do I explain this to her?