Answer: A compulsion.
Explanation: A compulsion is a behavior designed to reduce psychic distress or discomfort due to factors such as depression or anxiety. Compulsions are repetitive rule-bound behaviours that the individual feels must be performed in order to ward off distressing situations and Individuals engaging in compulsions typically feel an irresistible need to engage in the compulsive behavior.
Marty is exhibiting a compulsion by washing her hands repeatedly, because of the fear of germs that might make her ill and die.