In Susan Weinbrenner's book she writes about a strategy called "most difficult first". It essentially works like this:
all students who feel that they have mastery of the work on an assignment can opt for "most difficult first". They do the four most difficult problems and if they get them correct, they're done. If they don't get them correct then they go back and do the rest of the problems. Certainly gives kids who have carelessness issues a little more incentive to check over their work
The description in the book is easy to understand, not overly long and presented in a way that's hard to reject. It also talks about how a child who consistently is able to do this is going to need to be moved to more advanced work, but that's another story.
Maybe you could get ahold of the book and photocopy that section? Is part of her issue that she thinks a puzzle workbook is not 'work-ish' looking enough? Would she accept an alternative go-to resource like one of the Challenging Word Problem books from Primary (Singapore) Math?
Good luck with this. It certainly can't be a good use of her time to do endless repetitions of easily mastered materials!
