It doesn't work like that, at least not unless it's done illegally, in which case she can fight it at the LTB.

The future owner will have asked the present owner to give notice to the tenant on the grounds he wants to move in. The only way to fight this is to convince the LTB that the request is not sincere.

Redevelopment is another possibility and can be grounds for eviction, but seems unlikely from the story.

If the new owner purchased the house with the plan of flipping it in a couple of years (and not moving in or redeveloping), then the lease will survive the change in ownership.