The renunciation that every person makes when becoming a U.S. citizen (I renounce foreign potentates, etc.) is NOT the kind of renunciation that Canada is talking about. Only if your mother renounced her Canadian citizenship to Canadian officials (which hardly anyone did, except for people like Conrad Black or Ted Cruz, who did so for political reasons) would you not have inherited Canadian citizenship.
As of 2009, your mother got her citizenship back, retroactive to the day she lost it. (The fact that she may have been deceased doesn't alter that fact.) Therefore, if you are in the 1st generation born abroad, you are considered to have been born to a person who was a Canadian citizen when you were born.
I sent you the link to the video regarding the 2009 law. The people who "woke up Canadian" are mainly the thousands of people, mostly American, who were born to Canadian-born parents.
You are overthinking this, and don't seem to want to take "yes" (from the law firm, the online citizenship tool, and me) for an answer! Just fill out the application (answering the questions accurately, including the date your mother became a U.S. citizen), include your mother's birth certificate* and yours (full certificate containing parents' names), and send it in. In return, you will receive a Citizenship Certificate.
*"For Canadians born in the province of Quebec, only a birth certificate or a copy of an act of birth issued after January 1, 1994, by the Directeur de l'état civil of Quebec...[is] accepted."