And how about her business partner and friend Myrna Morgenstein (Barbara Sharma (https://www.ultimate70s.com/actor/Barbara_Sharma/-/-)) in the first two seasons?

And what happened to her best friend Sally Gallagher (Anne Meara (https://www.sitcomsonline.com/boards/showthread.php?t=336976))? She was with Rhoda and Brenda in just about (https://benjamonsterstv.blogspot.com/2021/02/episode-guides-rhoda-season-three.html) every episode (https://en.wikipedia.org/wiki/List_of_Rhoda_episodes) in Season 3 (https://jacksonupperco.com/2015/05/12/the-ten-best-rhoda-episodes-of-season-three/). The last we see her is on the 'New Year's Eve episode' (https://www.imdb.com/title/tt0685896/) in December 1976. Sally is never seen or mentioned again after that.

I remember watching the later episodes of Rhoda and to me, Susie, Myrna and Sally were victims of the Chuck Cunningham Syndrome, never seen or referred to again.

Funny but true story about Beverly Sanders; a few years back I ran into her at the market and told her I thought the best episode with her was "The Wedding Shower" in season one and she remarked, "every bitch in town was on that show"!