That is an interesting way to interpret the wording.
The relevant calendar years for the period the OP was talking about was: 2012, 2013, 2014, 2015, 2016, and 2017; six calendar years.
So, hypothetically, if she was not required to file on 2012, and 2013, due to residency, and maybe even 2014 (let's say she moved back to Canada late July 2014, and she has otherwise no ties to Canada).
And let's say that she did have to file in 2015, 2016, and 2017, but she did not.
Then she would still be fine?
So in this case, she would not have to file any taxes at all, just because of the fact that, in the 3 of the calendar years preceding the application, she was not required to?
I'm not sure if I would be comfortable making that argument to IRCC, and I'm not sure if that's how I would read the rule either.