Angelina Difficult conversations and please excuse my little "soul striptease" I hope I understand what I am writing if not ask me
Very interesting development. From what I can read between the lines, she doesn't want the access to the key when she went back home. At least for the trial period.
From what you wrote, I think she would be happier if you modify your agreement and give her the key just in a closed envelope. So she wouldn't feel trapped, but could explore how it is to not follow the wishes of her body. She would also have the opportunity to be very proud when she gives you the closed envelope back on arrival.
I really have the feeling that she would be happy with such an agreement. It would definitely give you much more information.