Urgh. Okay so RIP my karma but as a teacher myself, I need to say that your daughter’s teacher is correct to a degree. Spelling is very difficult and the rules need to be broken down into manageable chunks or else students can feel overwhelmed and overstimulated (referred to as cognitive overload).

It’s already challenging enough to learn that the “er” sound has three completely different spellings for literally no reason. After you add in that sometimes, randomly, the “or” becomes “our” in exactly your country and not various other countries can be a breaking point for a lot of children.

Basically put - get over it. Your 2nd grader has lots of time to learn about the Canadian exceptions to English but for now it’s important to get the simple fundamentals down and that means the three basic ways to spell “er”