As of right now, Big Machine owns all the master recordings of Taylor's old songs, meaning they (as well as her) have to give permission for the songs to be used in things like commercials and TV shows, and would be paid for it. However, in an interview with Billboard last year, Taylor revealed that she was saying no to all such requests.
"Every week, we get a dozen sync requests to use 'Shake It Off' in some advertisement or 'Blank Space' in some movie trailer, and we say no to every single one of them." she said. "I do want my music to live on. I do want it to be in movies, I do want it to be in commercials. But I only want that if I own it."