I wonder if this mirror creates a doppelganger of the person who sees it and then tries to kidnap them (rather than a sole creature trying to get out), it'd make sense a doppelgganger of the kid would make the mess in the mirror so another person would have to clean it, and then get kidnapped as well. But then, wouldn't the original kid be there on the mirror as well trying to get out?
That's why I think the kid is fine, but the sensei is imprisoned in the mirror. Hope Kaya can save her later, but considering they're in different classes I think that'll be unlikely.
Also, thank you very much for the scanlation and for going through the extra effort to identify and translate the obscured dialogue from the possessed(?) mom.