How to Lighten Medium Brown Hair

I was hoping someone could help me. My daughter has medium brown hair (level 5).  She wants to go a shade or two lighter for summer but does not want highlights.  I was wondering if there was a way to lighten up a shade or two without too noticible roots.  Or maybe highlighting with a lighter shade of brown if that would work and if so what color/level?  She doesn't want blonde or red.