Erin Moran, who has died aged 56 after suffering from cancer, was already a seasoned child star when she was cast in the role that made her recognised worldwide – as Joanie Cunningham in the American sitcom Happy Days. Joanie is the feisty kid sister of the clean-cut teenager Richie Cunningham, around whom much of the show’s action revolves, and takes a great interest in his attempts to attract girls.

Moran was only seven when she joined the children’s TV drama Daktari in 1968 for its final two runs, as Jenny Jones, an orphan given a home by the vet and conservationist Dr Marsh Tracy (played by Marshall Thompson) at his Wameru Study Center for Animal Behavior in east Africa. The popular adventure series was based on the 1965 film Clarence, the Cross-Eyed Lion.

Many guest roles followed for Moran on television before she was cast in 1974 as Joanie. Happy Days was inspired by George Lucas’s nostalgic 1973 film American Graffiti, celebrating the 1950s and early-60s teenage culture of rock’n’roll and cruising – young men driving around in cars in their quest to find girlfriends.

Erin Moran, centre, with other members of the cast of Happy Days. Photograph: Allstar/ABC

Ron Howard, who had appeared in the film, landed the starring role as Richie, with Tom Bosley and Marion Ross as his parents, Howard and Marion Cunningham, and Moran as his sister. However, this wholesome American family in 50s Milwaukee was upstaged by Henry Winkler’s cool, leather jacket-wearing Italian biker Arthur Fonzarelli, aka the Fonz, who liked to refer to Joanie as “shortcake”.

The programme’s creator, Garry Marshall, recognised that Howard and Winkler played off each other and resisted attempts to spin the Fonz off into his own series. Nevertheless, there were spin-offs. Laverne and Shirley and Mork & Mindy featured characters only briefly seen in Happy Days, but Joanie Loves Chachi (1982-83) gave Moran her own sitcom to reflect her character entering adulthood. Scott Baio played Joanie’s rock musician boyfriend, Chachi Arcola, Fonzie’s cousin in Happy Days, with the diner owner Al Delvecchio (Chachi’s stepfather), played by Al Molinaro, also switching to the new show, although it had limited success. “They put us up against Magnum, PI,” said Moran, reflecting on how it was scheduled “and that would shoot anybody down.”

Erin Moran as Joanie Cunningham

All three stars continued to appear in Happy Days until the end of its 10-year run. On screen, Joanie and Chachi married, and Moran and Baio were in a relationship off screen for a while.

Moran was born in Burbank, California, to Edward, a finance manager, and his wife, Sharon. One of six children – five sisters and a brother – she appeared in a TV commercial for a bank at the age of five and made her film debut, uncredited, as a girl on a tricycle, in the comedy Who’s Minding the Mint? (1967). Then, she was seen alongside James Garner and Debbie Reynolds in How Sweet It Is! (1967). While pursuing her acting career, she was educated at Walter Reed junior high school and North Hollywood high school. After Happy Days finished, Moran had guest roles in The Love Boat (1980-85) and Murder, She Wrote (1986), and appeared in the reality TV series Celebrity Fit Club USA (2008), but she struggled to find acting work. Her last credited screen role was in the horror-film spoof Not Another B Movie (2010).

Some members of the Happy Days crew in 2001. From left: Garry Marshall, Tom Bosley, Marion Ross, Erin Moran, Henry Winkler and Anson Williams.

Photograph: EJ Flynn/AP

In 2011, Moran, three of her Happy Days co-stars – Ross, Don Most and Anson Williams – and Bosley’s wife sued CBS, the show’s rights owner, in a $10m breach-of-contract lawsuit, claiming that they were owed money from merchandise sales. Eventually, each actor received $65,000.

Financial and personal problems had beset Moran over the years. Her first marriage, to Rocky Ferguson (1987-93), ended in divorce. She married Steven Fleischmann in 1993, but money troubles led them to sell their home in Palmdale, California, in 2010 and move into a caravan in Indiana with Fleischmann’s mother. Two years later, they were reportedly thrown out after Moran returned in a drunken state.

In 2009, the actor said she was writing an autobiography titled Happy Days, Depressing Nights. It has yet to be published.

Her husband survives her.

• Erin Marie Moran, actor, born 18 October 1960; died 22 April 2017