It feels, in fact, very fitting that the two have passed away almost hand-in-hand. When presenting Reynolds with a lifetime achievement award in 2015, Fisher quipped, "She has been more than a mother to me. Not much, but definitely more. Unsolicited stylist, interior decorator, marriage counsellor ..." Her mother may have seen their relationship differently.
Fisher's was a troubled childhood - a fact she regularly brought up to explain her struggles with substance abuse and bipolar disorder. "When I arrived, I was virtually unattended," she wrote in her autobiography. "And I have been trying to make up for that fact ever since."
Aged 13, she started smoking marijuana, and progressed quickly to harder drugs until a full-blown addiction blighted her twenties. As she once put it, "I am truly a product of Hollywood in-breeding. When two celebrities mate, someone like me is the result."
Reynolds was at the peak of her stardom when she and her husband, the suave crooner Eddie Fisher, had their daughter in 1956. She was only an 18-month-old baby when her father eloped with his wife's best friend, Elizabeth Taylor, in a scandal that exploded across the tabloids.
Reynolds and Fisher, America's original sweethearts, had respectively been maid of honour and best man at Taylor's wedding to the producer Mike Todd, who died in a 1958 plane crash. Reynolds found out about their affair in the worst way possible, when she phoned Taylor for a chat late at night, and Fisher answered the call.
She would recall: "I could hear her voice asking him who was calling - they were obviously in bed together. I yelled at him, 'Roll over, darling, and let me speak to Elizabeth'."
While their affair left Reynolds alone with two small children, she still put on a brave face and made up with her friend. "Elizabeth wasn't the kind of girl you should hate," she said in 2014. "You just had to make sure you kept your husband in the garage if ever she came to visit."
Fisher took a more caustic view later in life. As she put it in her one-woman show, "My father naturally flew to Elizabeth's side ... gradually, slowly, making his way to her front."
Reynolds's love life did not improve. A second husband left her financially ruined and humiliated her with prostitutes; a third left her bankrupt and admitting she had "very poor taste in men".
If Fisher turned her "Hollywood inbreeding" to her advantage in her comedy, the effect on her own personal life was more detrimental. "My mother wrote a blueprint, and I follow it to the letter," she said once, in an account of her own two failed marriages.
As her father all-but disappeared from her life, the young Carrie resented sharing her mother with the world. She even took to sleeping on a rug on the floor next to her bed when she was at home, creeping out quietly in the morning before the MGM star woke.
By the age of 10, she wrote, she had experienced the "horror" of realising she was not going to inherit the "confident and shining beauty" of her mother: "I was a clumsy-looking and intensely awkward, insecure girl ... I decided then that I'd better develop something else - if I wasn't going to be pretty, maybe I could be funny or smart."
Mothers and daughters often find themselves comparing lives and looks, but the rivalry was amplified tenfold in their case. Both had been catapulted very young to stardom: Reynolds landed her career-defining role in Singin' in the Rain at just 19 years old; Fisher was 21 when Princess Leia turned her into a global sex symbol.
"I thought I looked like a thumb," Fisher said about her looks growing up.
Whereas of her mother's radiant glamour, she recalled: "Every day, she'd go into one end of her wardrobe as my mom, and come out the other as Debbie Reynolds."
But the tide turned Fisher's way after Star Wars, and this rise in her profile coincided with the leanest years of Reynolds' professional life.
"My mother was no longer wanted in movies by the time she was 40," Fisher told Oprah Winfrey in 2011, when the pair appeared together. Reynolds said: "People used to call her Debbie Reynolds' daughter; now they call me Princess Leia's mother!"
It wasn't until Fisher's own career took off that their mother-daughter strife became a public feud. Carrie dedicated Postcards from the Edge to Reynolds, who was affronted by the film. "I love to get up and entertain at parties ... and Shirley put a lot of my traits in the part. But I don't have the disease of alcoholism, thank God," she told the Daily Telegraph.
"I could never drink vodka the way she did in the movie. I don't even like vodka."
The insult was compounded when Reynolds was told she was "not right" to play the mother, with Shirley MacLaine getting the role she had been "creating - admittedly unwittingly - for my daughter for decades".
The darkest phase of their relationship came when Reynolds' second husband, businessman Harry Karl, gambled away their entire joint fortune, leaving her, in her own words, "flat broke". At the same time, Fisher was steeped in her mental health struggle.
At this period in the eighties, mother and daughter were not in contact, as Fisher continued to undergo electroconvulsive therapy. "I did not want to be Debbie Reynolds' daughter," she said of those years.
Reynolds had her own view, telling Winfrey in 2011: "All I could do is love her, and always shall."
It was to be at least 10 "very painful, very heartbreaking" years before the pair began to talk again. As Fisher battled depression, she recognised her mother's involvement in Thalians, a mental-health charity founded in 1955, and their relationship thawed. The numerous public appearances together that followed suggested that bygones had fully become bygones.
"She's an extraordinary woman. Extraordinary," Carrie said of her mother, when promoting her final memoir, The Princess Diarist.
"There are very few women from her generation who just kept a career going all her life, and raised children, and had horrible relationships, and lost all her money, and got it back again ... she's someone to admire."
"It took, like, 30 years for Carrie to be really happy with me," Reynolds recently told People magazine.
"I don't know what the problem ever was.
"I've always been a good mother, but I've always been in show business ... I don't bake cookies and I don't stay home."
Fisher, it turned out, did bake. Their final on-screen appearance together will see her carefully carrying a souffle to her mother at home next door, in a touching role reversal that could sum up the final chapter of their changed relationship.
