Perhaps because "work" is on the grade 3 spelling lists. I kid you not. I just looked it up and on 2 different spelling lists for 3rd grade is the word "work" and other words similar in complexity.

http://www.all-about-spelling.com/spelling-list-for-3rd-grade.html

OH ... and "isn't" is on the list as well so maybe that is when she will learn the concept of it.

My DD's school teaches spelling words such as "Baccalaureate" to 1st grade which I was shocked to learn but the teacher said it was on par with 3rd grade level. I don't know what 3rd grade school she is referring to if "work" and "isn't" is part of the generic lists out on the internet.