Taylor Swift does not fear a challenge. She's broken records then broken those records; taken Grammy snubs as a sign she just has to work harder; mounted probably the most physically exhausting tour of all time. But in writing a song for Toy Story's cowgirl Jessie, she's set herself a deranged task: how could anyone outdo Randy Newman's devastating When She Loved Me, Jessie's song about being abandoned by her owner, Emily, from Toy Story 2?