In your sister's case, technically the hospital would be liable for damage she suffered as a result of the hospital's employee's failure to properly transport and secure your sister.  However, one of the elements of a personal injury or medical malpractice claim is physical damage which required medical care.  If your sister's only injury is some bruises, it does not appear that she has significant enough damage to pursue any type of claim against the hospital.  In large part, personal injury and medical malpractice claims are based on the amount of medical bills involved.  In this instance, it sounds as if your sister had no additional bills and required no medical care as a result of this incident.  As such, she does not have much of a claim to pursue.