I've switched the format of this chat as the chat interface seems to be having technical issues as I could not see your response, however I can see them now.
If she was sent home by the manager, then she did not "fail to work her shift". I expect that in order to cover themselves, they'll likely try to claim that there were "performance issues" which is a typical fall back position where employers have jumped the gun in firing an employee.
Ultimately, there could be a complaint with the labour board for terminating her because she wouldn't perform "optional" overtime, which is essentially what happened. However this would require retaining a lawyer to fight it and lead to some expense, which in the end may not be worth the cost and stress involved.
If they are terminating her, they'd generally need to provide her with a couple weeks pay as severance if they're terminating without cause, but again I expect that they'll have some excuse as to why they've terminated her, claiming cause.
This doesn't sound like a place your daughter would want to go back to now anyhow.
You may want to send them a letter detailing what occurred and the fact that she in fact worked her scheduled shift up until the time she was told to go home, which means that the employer ended her shift early, she didn't leave before her shift was over then. You could ask for appropriate severance and make them aware that the actions of their manager are in contravention of employment standards and see what they come back with. It's possible that nobody's ever called them on this before, so the fact that you reference employment standards in a letter may make them think twice about their actions.
If you'd rather pursue it, I'm happy to help get you referred to a local lawyer with whom you can consult.
If you have any further questions, or require clarification, please let me know as I am happy to discuss this further.