Labour Law Case in Medical Field

let me share a background of the case before asking questions

The employee who is charged (Lets call her employee OD) is working as ODA (Operating Department Assistant). Her core functions includes assisting the Doctor with preparation of threatre like instruments and mechinery prior perfroming the operation. 

Last in November the Unit Manager (Lets call her sister A) requested her to mentor new employee Sister B(Lets call her sister B).

According to their designated ranks Sister B is supposed to be senior. Shes more qualified with years experience in Theatre. Employee OD has 7 years experience meaning Sister B is senior because of experience and qualifications. 

OD is supervising the Sister B in line with instructions from Sister A. OD leaves the Theatre as the case was supposed to be completed. After leaving Sister B  was supposed to count the swabs ensure that all the swabs were removed from the patient. She fails to account for one swab because of human error.

Now the two employees are in trouble but Sister B decides to resign even before a discplinary measures can be instituted against her. OD is charged with Negligence for failing to supervise Sister B. 

In a disciplinary hearing OD is found guilty of negligence because she failed to Supervise Sister B. Shes served with final written warning. Does She have a leagl leg to stand on? if yes can she ask for a review or appeal?