Normally, upon entering the home as an honored guest, the women of the house would serve food and beverages and generally tend to the guests. Here, the oldest woman in the house was ill and unable to serve. What a faux pas! But Jesus comes to save the day with his power of authority, ordering the woman to get up anyway and serve them. Hooray! The day is saved!
The scene here isn’t given words said, but I could imagine Jesus said something like,
“Do you have a fever? Your fever is irrelevant. You serve God now. Get up. Get busy.”
The authority brag continues: he has so much authority, he can even make women work for him when they claim to be sick.
Looking at this from the “Two Jesus” theory brings a little more clarity. Shy Jesus has just been ejected from the synagogue, and he goes to the house of one of his followers. The mother-in-law probably disagreed with this Zealot activity, and likely would have preferred to avoid conflict entirely. But Shy Jesus convinces her to go along with the rebellion, so he was either slick tongued or manipulative.