She ate corn kernels, wheat seeds, and bird seed. She probably ate berries also, although we didn't try them with her. However, when the weather turns cold, robins must switch to eating almost nothing but fruit. When it's very cold, a robin keeps warm by shivering, and the sugar from berries gives it plenty of energy to shiver. When robins over-winter in northern places, they usually stay near fruit trees, and during cold snaps in spring robins may return to them.
Fruit also gives robins energy to fuel their long migration.
Cold weather keeps fruit fairly fresh, but eventually it gets moldy just as food left too long in a refrigerator does. And old fruit slowly ferments, which means that the some of the sugar changes to alcohol. If robins eat too many fermented berries, they can become confused and clumsy, and sometimes crash into things or get killed by predators. So as soon as any fresh food becomes available in spring, robins desert the old berries and concentrate on worms and any early bugs until the trees leaf out and new fruits start to grow. Worms have lots of protein, so are nutritious for robins.