Possible Clues:

• Chatter behind gym with US stars
• Mythical mount that flies
• Winged horse of Greek myth
• Margaret, like us, on high horse
• Lots of fun in gym with American stars
• Horse off to a flying start?
• Day Lewis's description of Margaret as American horse?
• Mythical horse with feathers
• A mount in the Classics?
• Fish and flying horse