Taylor Swift's role in "The Giver" is tough to explain, but she's essentially the forebear to Jonas (Brenton Thwaites), the young protagonist tasked with uploading every memory of his dystopian, brainwashed civilization into his brain. The movie flashes back to Rosemary's (Swift) turn as "the receiver," and in a holographic haze we watch as she interacts with "the giver" Jeff Bridges. She teaches him some music on the piano and they bond.
There you have it. Earnest and buttoned up and music-loving. Well done, casting department.