Petra was a citizen living in the same town as Doctor Schumann. She was widowed and her son left her five years ago. However, she still made Goulash for two people out of habit, which was one of the reasons why Dr. Schumann always stopped by. During Dr. Tenma's visit, he diagnosed her with a subarachnoid hemorrhage and operated on her. Her son wanted to catch Dr. Tenma so his promotion would be secured, but Schumann appealed to his conscience by saying that the man saved his mother. (Source: Monster Wikia)