I had just read here very, very recently, that doctors were warning her to lose weight, or she was going to die. Not sure just how true that was, but given the timing, it seems plausible.
Still, sad loss. In addition to being half of Laverne & Shirley, she was also Oscar's loyal secretary Myrna in the 70s version of THE ODD COUPLE, and she was also one of only two actresses who auditioned to be Witchiepoo on H.R. PUFNSTUF, ultimately losing to Billie Hayes.