Informally talk to the owner, more in a "I think your daughter is not very happy with her shifts during the week; maybe we can find a solution which is compatible with school and social life" way than in a "let's discipline her" way.
If the owner realizes he may be losing money because of this (which is what happens if you deliver pizzas late), he may have a word with his daughter.
EDIT: One aspect which I forgot is the following: You consider the daughter to be the special, protected pony. However you don't know if she ever liked the job or if her dad decided that she is old enough to help in the family business.