Thorndike's first stage role of the 1960s was Lotta Bainbridge in Coward's
Waiting in the Wings; she and
Marie Löhr played the lead roles of two residents in a retirement home for actors and actresses, perpetuating, and finally resolving, an ancient feud. She said of it, "I loved that play. It's the most lovely modern play I've played", but the piece was not a great box-office success and closed after 188 performances. In 1961 Thorndike played the longest part of her career, the title role in
Hugh Ross Williamson's
Teresa of Avila, about the
eponymous saint. She thought it "the most thrilling part I've been offered since Saint Joan", but Williamson's script, even after extensive revision by Casson, proved disappointing. Reviews were enthusiastic in their praise of Thorndike's performance, but neither the critics nor the public liked the play, which closed after six weeks. The critic
J. C. Trewin wrote of "the most remarkably complete production – in my experience at least – of any play in our period". He called Thorndike's nurse "a miracle of gruff tenderness". The production was acknowledged as the highlight of the festival, and was revived the following year. Between the two stagings Thorndike appeared for the first time in a musical – playing the formidable Miss Crawley in an adaptation of
Thackeray's Vanity Fair. The piece received bad reviews.
The Guardian said that at her age Thorndike "should have known better than be caught up in this piece of prolonged nonsense", although
The Times found consolation in her "blazingly theatrical figure" who "stamps every line with comic authority". Olivier moved from Chichester to become the founding director of the
National Theatre in late 1963. He included
Uncle Vanya in his first season, with many of his Chichester cast reprising their roles, but Casson, by this time in his late eighties, declined, and Thorndike did likewise. At the
Duchess Theatre in January 1964 she appeared as the Dowager Countess of Lister in
William Douglas-Home's play
The Reluctant Peer, a comic fictionalisation of the author's
elder brother's recent renunciation of his peerage so as to be eligible for the premiership. Once again, Thorndike's notices were better than those for the play.
Bernard Levin wrote, "she gets her fangs deep into the meatiest part she has had for years" and praised "the relish and zest she brings to her playing". She thought the critics were wrong to dismiss the play – "they only want avant-garde and classics now" – and was sorry when her contractual commitments forced her to leave the cast six months into the eighteen-month run. , 1972|thumb|left|alt=old white woman, seated in front of a well-filled bookcase After appearing in two successive box-office failures –
Arthur Marshall's Season of Goodwill (1964) and
William Corlett's
Return Ticket (1965) – Thorndike rejoined Casson in what turned out to be their last West End production together, a revival of the classic black comedy
Arsenic and Old Lace. With
Athene Seyler co-starring as her equally well-meaning and homicidally lunatic sister, Thorndike enjoyed herself, the critics were enthusiastic, and the play ran from February to November 1966. Thorndike appeared no more on the London stage after that. At the
Yvonne Arnaud Theatre, Guildford, in January 1967 she played Claire Ragond in
The Viaduct, and at the same theatre in February 1968 she appeared as Mrs Basil in
Call Me Jacky. Later in that year she toured as Mrs Bramson in Emlyn Williams's thriller
Night Must Fall. The television was not her favourite medium – she found it restricting – although she had a success in 1965 as Mrs Moore in a BBC adaptation of
E. M. Forster's
A Passage to India. Forster congratulated her on her performance, but she replied, "I loved Mrs Moore, but I am not wild about TV as a medium to express her! She's bigger than that". Casson died in May 1969, and Thorndike's only stage role after that was in the inaugural performance of the theatre named in her honour, the
Thorndike Theatre, Leatherhead, in October of that year, as the Woman in
There Was an Old Woman by John Graham. She was appointed
Member of the Order of the Companions of Honour in 1970. Her last public appearance was at the National Theatre's final night at the Old Vic in February 1976, where from a wheelchair she acknowledged the applause of her fellow members of the audience.
Brian Harrison recorded an oral history interview with Thorndike, in December 1975, as part of the Suffrage Interviews project, titled
Oral evidence on the suffragette and suffragist movements: the Brian Harrison interviews. In it she talks about the progressive nature of the theatre, and her freedom as an actress as well as her support for women's suffrage. Thorndike and Casson had long lived at
Swan Court, Chelsea, where she died on 9 June 1976, aged 93. ==Reputation==