She's paid to play music and she's good at that, people who go to this concert probably don't support Hillary Clinton, they want a concert. Believe me, country music fans are not voting Democratic, I'm a fan of country myself.
Many real country musicians, as opposed to the 'new country' musicians are Democrats. Robert Earl Keen, Kelly Willis and Bruce Robinson, probably Kacey Musgraves, Willie Nelson most of the time, Nanci Griffith, Steve Earle, John Mellencamp and Roseanne Cash, just to name a few.