Based on the information given, she is suffering from schizophrenia.
Schizophrenia simply means a disorder that affects the ability of an individual to think and behave clearly. In such a case, people interpret reality abnormally.
Therefore, since she believes that aliens from another planet have removed her stomach and are watching to see how long it takes her to grow another, she's suffering from schizophrenia.
People often behaves in odd ways due to some medical conditions. Higgins is most likely suffering from schizophrenia.
Schizophrenia is simply known to be an extreme form of mental disorder in which a person do interpret reality in an abnormal way.
It can bring about some mix-up of hallucinations, delusions, and high disordered thinking and behavior that hinders daily functioning. It can be monitored medically.
