I have also bounced this off of our DH Team and they have come back with the following:
The question is quite complicated as the helper shouldn’t have followed her employer to Canada if they were already relocating at that time.
In this case the helper should report to Hong Kong Immigration and explain what happened.
It looks like the employer hasn’t sent any termination form “declaring their relocation” as they were still asking for the helper to write a break contract letter and providing for one month salary in lieu of the notice.
Immigration will be the one to decide on what will happen to her working visa.
Hope that helps!