A simple updo would be perfect! Preferably one that she could redo herself if the need arises. Just gather the hair into a low ponytail (but without a hairtie) and twist the length all the way to the ends. Then pull the twisted ponytail up and secure at the crown with bobbypins or use a claw clip to hold the twisted ponytail to the back of the head. Arrange the ends around the top of the head however you wish and you're done.

When I was very young, my mother used to twist my hair up like this and secure it with bobby pins for when I was going to take a bath without getting my hair wet. But it actually makes for a simple updo which can be cute if done right. Good luck!