Peter's mother-in-law was the mother of Peter's wife. Peter's mother-in-law was sick, and Jesus healed her. She served Jesus and his companions afterwards.
When Jesus went into Peter’s house [in Capernaum], He saw Peter’s mother-in-law lying sick in bed with a fever. He touched her hand and the fever left her; and she got up and served Him.— Matthew 8:14–8:15 (AMP)
And immediately they left the synagogue and went into the house of Simon [Peter] and Andrew, accompanied by James and John. Now Simon’s mother-in-law was lying sick with a fever; and immediately they told Him about her. Jesus went to her, and taking her by the hand, raised her up; and the fever left her, and she began to serve them [as her guests].— Mark 1:29–1:31 (AMP)
Then Jesus got up and left the synagogue and went to Simon’s (Peter’s) house. Now Simon’s mother-in-law was suffering from a high fever, and they asked Him to help her. Standing over her, He rebuked the fever, and it left her; and immediately she got up and began serving them [as her guests].— Luke 4:38–4:39 (AMP)