Kelly Clarkson is from Texas, and while that doesn't guarantee she will be a country singer, her roots do come through in her music. She is primarily a pop singer, because that it what brought her to fame on American Idol, but she has performed country music as well, singing with the likes of Reba McIntyre.
On the voice she's continually saying she's as country as Blake Shelton, But I totally disagree. I've enjoyed some of her music but just because she's done songs with some country singers doesn't make her country. Also just being related to Reba doesn't make her any more country. Not country!
I consider Kelly Clarkson to be a pop singer rather than a country singer. I think she has a voice and personal style that could definitely adapt to country singing, but I see her as a pop singer. I have only heard pop songs from her, and definitely think she fits this style very well.
There's a difference between being able to sing country music reasonably well, and being a country music singer. Kelly Clarkson is talented, but when she sings country she makes it into the easy listening version of country. It doesn't have anything near the authenticity that you get from a real country music star.
Although Kelly Clarkson is a talented singer, she is not a country singer. Her music is routinely played on Top 40 radio stations and most of her songs have obvious pop influences. She started her career as a pop singer and while she may eventually cross over into the country music world, she is not currently there.