Why does the daughter leave the old couple in "The Crane Maiden"?

When she started making fabric for them, she made them promise not to look inside the room she would make them in. They broke their promise and found out she was a crane the old man had saved earlier in the story. Due to the fact she could not trust them, she was forced to leave for her own safety. I'm sorry if this answer isn't accurate, I haven't gone over this story in a very long time.