She did not actually quit the show.
"Get Smart" was cancelled after five seasons in 1970. While there were rumors of tension between Feldon and co-star Don Adams, the show's cancellation was due to declining ratings, not any personal disagreements.
It's possible you're misremembering or confusing information. Could you provide any more context about the lady and the show you're referring to? This could help me understand your question better and give you a more accurate answer.