I had the same reaction.
It also feels written by someone with little experience in how fast kids learn languages. Any immigrant kid that transferred to my school in elementary school could speak perfect English within a year. A kid being raised here but not speaking good English because her mother only spoke Japanese at home is just wild.
well now that you mention it, that definitely makes no sense
first and foremost, if canadian english was her first english, she'd have learned it by the end of like, two years of school, tops (unfortunately my evidence for this is entirely anecdotal, being raised in a mandarin-speaking household, but i'm sure i could find a study if i dug deep enough)
if, for some reason, she learnt some other dialect of english first, as long as interaction w/ canadian english occurs before ~8 years old, she'd also acquire canadian english
there are plenty of case studies on this matter, such as Chamber 1992 (which i can't for the life of me find a copy of? but my sociolinguistics prof cited it way back when so i'll trust him on that matter. UPDATE: i found it, i was just searching under jack chambers instead of jk chambers, his pen name), Tagliamonte & Molfenter 2007, and Trudgill 1986
tbf all these case studies have to do with children moving from one english speaking country to another (canada to england, ottawa. canada to york, uk, and britain to australia respectively)
in conclusion, children acquire language bloody fast, don't underestimate them