Lena's real mom, Emily, knew that this was not the truth, but she also knew that Vaclav was not lying.
Vaclav knew that he was telling the truth.
Lena knew that it was a lie, but she loved it and believed it, like a fairy tale, like a song, like a bedtime story, like a magic trick.
She loved Vaclav until it became the truth and so it was.