I think that the show chose not to show what happened because, realistically, her parents were probably killed. The history of the residential schools is extremely horrific, and includes the deaths of many children (who were mentally and physically abused, and stripped of their native identities). We saw those men threaten Ka’Kwet’s parents with guns; hell, one of them shot her father. They treated those children like they were less than human, and I can’t imagine they wouldn’t have seen their parents in the same way.
What we need to focus on with Ka’Kwet’s storyline is that the actions taken by the government back then have a lasting impact to this day for indigenous people.
“The history of residential schools has been identified as having long lasting and intergenerational effects on the physical and mental well-being of Indigenous populations in Canada. “
For more information on the residential schools and their lasting damage:
https://www.thecanadianencyclopedia.ca/en/article/residential-schools
https://publichealthreviews.biomedcentral.com/articles/10.1186/s40985-017-0055-6