I guess she divorced Mike and ended up on CHiPS Season 3 E 19.
I was watching and I thought that smile looked familiar. Looked her up and sure enough its Meredith MacRae.
https://www.imdb.com/title/tt0534494/?ref_=ttep_ep_19

Thats not all. She died of brain cancer. Let her body be used as research. Sounds like a horrible death too.

Poor thing. Like Cousin Milly from Gurney.

https://en.wikipedia.org/wiki/Meredith_MacRae#

Best remembered for her 4 seasons as one of the stars of Petticoat Junction (1966-70), many fans of which are aware that she passed away while still in her 50s; so much life ahead that was very sadly never lived. Memory Eternal.

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Poor thing. Like Cousin Milly from Gurney

Milly of Father Knows Best, here we see Susan Oliver in her
memorable My Three Sons episode:

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Memory Eternal

Meredith MacRae was a classy lady always! Seems like she was a very nice and unaffected (no huge ego) actress. I have always liked her.