Anything she likes to eat that will work in a cold frame. If she loves carrots, grow those if the soil is OK for that. If she likes many vegetables, and there is room, try a few things she likes.
In the spring/summer, if she has a space outside of the cold frame, if there is room for melons or pumpkins that can produce fruit in your conditions, try that. Small pumpkins suitable for a pumpkin pie provide a nice treat!