From 1955 until 1993, Nichols worked for Warner Bros., Disney, UPA, Fleischer, Snowball, Patin, TV Spots, Creston, Eagle, Hanna-Barbera, Marvel, Universal and Graz Entertainment.
She was also known as Margaret Flores Nichols and Margaret Grewell.
Nichols directed the TV series Transformers (1985–86); The Glo Friends, Potato Head Kids, InHumanoids and Moon Dreamers (all 1986); My Little Pony ‘n Friends (1986–87), and Fraggle Rock (1987).
She served as an animation director for the series Muppet Babies (1985–88), Defenders of the Earth (1986), Spacecats and Bucky O’Hare and the Toad Wars! (both 1991), Tom & Jerry Kids and The Addams Family (both 1992), The Pirates of Dark Water (1992–93), and Droopy, Master Detective (1993). In addition, she was animation director of the TV movies Solarman (1986), Pryde of the X-Men (1989) and I Yabba-Dabba-Do! (1993), along with the 1986 theatrical films Transformers: The Movie and My Little Pony: The Movie and the 1987 video G.I. Joe: The Movie.
As an animator, Nichols worked on the series The Pebbles and Bamm-Bamm Show (1971); The Flintstone Comedy Hour (1972); Jeannie and Speed Buggy (both 1973); These Are the Days and Partridge Family 2200 A.D. (both 1974); The Tom & Jerry Show (1975); The Mumbly Cartoon Show and The Scooby-Doo/Dynomutt Hour (both 1976); The All-New Superfriends Hour and CB Bears (both 1977); Scooby’s All Star Laff-a-Lympics (1977–78); Jana of the Jungle, Challenge of the Superfriends and Dynomutt Dog Wonder (all 1978); The Godzilla Power Hour (1978–79); The World's Greatest Superfriends, Scooby-Doo and Scrappy-Doo and Casper and the Angels (all 1979;) Trollkins and The Kwicky Koala Show (both 1981); Smurfs (1981–84); Jokebook, Shirt Tales and Pac-Man (all 1982), and The New Scooby and Scrappy Doo Show and The Charlie Brown and Snoopy Show (both 1983).
Also, Nichols was an animator on the 1974 ABC Afterschool Special Cyrano, along with the ABC Weekend Specials The Puppy Saves the Circus (1981) and Miss Switch to the Rescue and Bunnicula, the Vampire Rabbit (both 1982). She animated the TV shorts and TV-movies Clerow Wilson’s Great Escape (1974), The White Seal (1975), A Flintstone Christmas (1977), Christmas Comes to Pacland (1982), Is This Goodbye, Charlie Brown? (1983) and It’s Flashbeagle, Charlie Brown (1984), in addition to the 1987 theatrical movie Rock Odyssey.
A key assistant animator on the 1973 movie Charlotte's Web, Nichols was an assistant animator on Who Framed Roger Rabbit and Disney’s Oliver & Company (both 1988). She was a character animator on the 1982 theatrical film Heidi's Song and a guest animator on Chuck Jones’ 1975 TV-movie Yankee Doodle Cricket.
Nichols was a sequence director on the TV series Robotix (1985), G.I. Joe (1985–86), Jem (1985–88), Transformers (1986–87) and The Little Wizards (1987), as well as the 1985 video Bigfoot and the Muscle Machines and TV-movie The GLO Friends Save Christmas.
Her first screen credit was as a layout artist for the 1970 TV-movie Uncle Sam Magoo. Nichols was a background and layout artist for the 1971 musical film Shinbone Alley.
At Disney, Nichols was a key clean-up artist for the movie The Black Cauldron (1985), and a character key for The Little Mermaid (1989) and The Rescuers Down Under (1990). She was a timing director and sheet timer for X-Men (1992–94) and a timing director for the 1994 TV series The Tick.