There’s a very comprehensive post over here about the life of Kate McGarrigle. I’m not even going to try to compete with it.
Like many of my generation, Kate McGarrigle is part of my experience as a Canadian, whether you know it or not. I only became familiar with her as an artist in my adult years, mostly due to her children, Rufus and Martha Wainwright, but I grew up with her voice(and that of her sister, Anna) in the NFB short, the Log Driver’s Waltz. Kate is part of the wallpaper of Canadian life. Read about her at the link above.