'Ainsley' was not the real Ainsley's soul, just an illusion projected from Ainsworth's deepest feelings.
Of course she couldn't just say she would take back the body.
Whatever she said was actually just a bluff to shake Ainsworth's mind, entangling in a psychological war.
But now that Ainsworth believed in her own words about staying and helping the Sloan Family to flourish as a way to pay for stealing the body, 'Ainsley' had nothing to do.
Just..why? Why could Ainsworth have such a mindset to do everything for the family even if she had to leave in the end?
Of course, that might not happen in reality, but the moment Ainsworth said that she was willing for that to happen, the doubt, guilt and other negative feelings in her heart vanished.
Since the illusion reflected Ainsworth's pitiful side, she could no longer maintain her form.
She was defeated thoroughly.
