She should write up a registered letter to her employer today saying what she signed last night was under duress, and is not an accurate reflection of her behavior. She should tape $2.50 to the letter as repayment for her single incident of dishonesty.
Then, she should not show up to the next busy shift. Instead, she should find employment elsewhere.
This is a bad employer who does not value or trust it's employees. It does not deserve good people.