Taissa Farmiga has appeared in several seasons of American Horror Story. I think it's around three or four, but you'd better double-check for the exact number.
Her versatility is another factor. She can play different types of characters, from the innocent to the more devious. For example, in different seasons, she has adapted to various storylines, whether it's a haunted house scenario or a witch - centric plot. This flexibility has kept the audience interested in her characters and thus in the show as a whole.
One of her memorable roles was in 'American Horror Story: Murder House'. Her performance added depth to the complex and often spooky storyline. She was able to bring out the vulnerability and strength of her character.