What happened to Mr. Cadaver?

After relocating to Ohio with her father, Sal particularly resents Margaret Cadaver who seems to relate well with her father. She is convinced that Margaret is intent on taking her late mother’s place in her father’s life and sees no good whatsoever in her. Therefore, when Phoebe tells her that Margaret likely conspired with her blind mother to kill Mr. Cadaver, she detests her further.
The truth about Mr. Cadaver’s death is revealed later by Mr. Birkway, Margaret’s brother. He tells Phoebe and Sal that Mr. Cadaver died in an accident; a drunk driver hit a car which Mr. Cadaver and his mother-in-law were in. Whereas Mr. Cadaver died, his mother-in-law survived but lost her sight. Coincidentally, Margaret, a nurse, was on duty at the hospital when her husband and mother were rushed in as casualties, and she witnessed her husband’s demise. After this revelation, Sal becomes empathetic towards Margaret who as it turns out is actually a pleasant person who has been through a lot.