Das sagt die englische Wiki:

"Jo Marie Payton-Noble, the original actress who played Harriette (originating the character on Perfect Strangers), left in December 1997 (prior to the final season) because she was unhappy with the emphasis placed on Steve Urkel and his sub-characters (Stefan, Myrtle, O.G.D., etc.). Many believe this is a case of a series jumping the shark. When a Parade viewer asked why she was replaced, Jo Marie Payton-Noble stated that she also wanted to write or direct an episode, but was never permitted to do so. She was replaced in the final season by Judyann Elder."

Hoffe das hilft.