basically for the longest time the biggest thing Im@s did with Karen was she got sick one time and had to stay home, then eventually she got popular and was put in the anime after years of people joking that her whole character is someone on death's door. Now they integrated her referencing the one time she got bedridden a lot.
Its a bit like how Sachiko wasn't meant to be an idol that gets the bulli and cries a lot, but the fans reacted that way the minute they saw her, and voila.