Good catch! You are absolutely correct. As someone who once majored in Journalism, worked as a proofreader, and wrote and edited copy for advertisements and brochures for several years, I ought to know better.
However, I should point out that the number 35 in written form should be hyphenated as "thirty-five". Also, there is no antecedent for the pronoun "it" in your sentence, "She was never off duty when it came to correcting my grammar!"
I'm just having fun with your post, too. :-)
Once at a homeschool meeting, a newspaper reporter came to talk to us about teaching our children to write well. However, his words were "write good." A few mothers snickered, and the guy looked slightly embarrassed. But, as someone who worked proofreading and editing copy written not only FOR schoolteachers but BY schoolteachers and other educated people, I understood that everyone makes an error now and then. I know I certainly do. :-)
Correction: Your sentence passes. The antecedent for "it" in that sentence is the word "duty". The words "off duty" were not hyphenated, so I guess "it" could refer to "duty". My mistake.
For the record, I really don't care about the use of pronouns or hyphenation in the posts on this forum. Just having fun because I know you're the grammar cop here.