In the decades since her death, Frederick has steadily attracted a posthumous cult following for her collection of work in motion pictures and television.

Some of her better-known performances include her roles in films such as Nicholas and Alexandra (1971), The Amazing Mr. Blunden (1972), Henry VIII and His Six Wives (1972), and Voyage of the Damned (1976).

Wilde had been looking for a young, unknown actress to star in his film adaptation of the best-selling post-apocalyptic science fiction novel The Death of Grass by John Christopher.

Wilde first saw her when she came to work with her mother to pose for some test shots, and he immediately was smitten by her beauty, charisma, and bubbly personality.

Represented by the talent agency Hazel Malone Management, Frederick became a teen idol among the British public in the early 1970s, and was seen as the next Hayley Mills and Olivia Hussey.

Frederick then signed a cosmetics contract with Mennen, and became a spokesmodel for Protein 21 shampoo, starring in nationwide print and television advertising campaigns.

Frederick was also first runner-up for the role of Saint Clare of Assisi in the Franco Zeffirelli production of Brother Sun, Sister Moon (1972),[9] which ultimately went to Judi Bowker.

Some of the shows in which she appeared were Wessex Tales, Follyfoot, The Generation Game, and an adaptation of The Canterville Ghost where she first met David Niven, who became a lifelong friend.

The series featured a huge cast of prominent and rising British actors, including Anthony Andrews, of whom she played the love interest.

Frederick landed a role in the Spanish romance film A Long Return (Largo retorno, 1975), where she played her first grown-up character.

Following Sellers' death, his controversial will, the ongoing feuds with her stepchildren, and her short marriage to David Frost, Frederick became a figure of hate and ridicule in the press and other media.

Writer Stephen Bach said of their relationship: "I noticed as he [Peter Sellers] rose, that not once in the long talkative afternoon had he let go of Lynne's hand, nor had she moved away.

[20] The tension between them increased after the box-office and critical failure of The Prisoner of Zenda (1979), followed by negative tabloid reports of rumours of drug use, infidelity, domestic abuse, and other alleged conflicts.

[22][23] Despite appeals from a number of Sellers's friends to make a fair settlement to the children, Frederick allegedly refused to give her stepchildren anything due to their rocky relationship with her and Peter.

Her supposed eagerness to remarry so quickly after Sellers's death caused a loss of reputation in the public eye, and was one of the major factors in her blacklisting.

After her divorce from Barry Unger, Frederick lived in a Los Angeles mansion that had previously been owned by the actor Gary Cooper.

Five days after the wedding, Iris spoke out against the marriage in an interview with the Daily Mirror: "Time will tell, but I think Lynne has made a terrible mistake.

In 1972, while in her late teens, Frederick became involved with Curzon House Club casino owner Julian Posner, who like Sellers was 30 years her senior.

Grant also stated that she witnessed all the men on set, including the film's director Stuart Rosenberg, make salacious passes at Frederick, all of which she rejected.

[35] Julie Andrews stated in her 2019 autobiography Home Work: A Memoir of My Hollywood Years that she suspected her husband Blake Edwards was having an affair with Lynne (who was married to Sellers at the time) during production of Revenge of the Pink Panther (1978).

She later had a falling-out with Edwards and Andrews after successfully suing them for their involvement with the film Trail of the Pink Panther (1982), claiming that it insulted Sellers' memory.

"[39] Although not gay herself, Frederick was known for being a blunt and outspoken advocate for same-sex relationships and LGBT rights during a time when it was considered highly taboo.

[40] In a 1975 interview, she expressed some agnostic views when she was asked about a progressive Catholic priest's response to the pope's declaring premarital sex a sin.

[42] After her own death in 1994, she left individual sums of $250,000 to the British Heart Foundation and the Middlesex Hospital in London as tribute to Sellers.

In the 1995 revision of his 1994 book The Life and Death of Peter Sellers, Roger Lewis claimed that "there is yet to find a single person to say a good thing about Lynne".

[19] Other people who have voiced unfavorable views of Frederick include Spike Milligan, Britt Ekland,[47] Roger Moore,[48] and Wendy Richard.

"[50] Over time, views toward Frederick's image gradually shifted, and she soon gained a cult following[51] through her films, and has been described as one of the most promising, talented, and beautiful young British actresses of the 1970s.

[52] Many credit the negative events in her life (the loss of her acting career, blacklisting in Hollywood, and untimely death) to her marriage to Sellers.

[20] Other people who have defended or come forward with positive recollections of Frederick over the years include Judy Matheson,[54][55] Françoise Pascal,[32][33] John Moulder-Brown,[56] Mark Burns, Fabio Testi, Malcolm McDowell, and Graham Crowden.

[9] In 1982, Frederick's screen appearance as Catherine Howard from the film Henry VIII and His Six Wives (1972) was used on the cover art for the 1982 novel The Dark Rose by Cynthia Harrod-Eagles.