Tree elaborated this into a great tableau... Cleopatra, robed in silver, crowned in silver, carrying a golden scepter and the symbol of the sacred golden calf in her hand, went in procession through the streets of Alexandria, the ragged, screaming populace acclaiming the Queen, half in hate, half in superstitious fear and joy as she made her sacrilegious ascent to her high throne in the market-place.

In January 1908, she starred with Beerbohm Tree at His Majesty's Theatre in J. Comyn's new play The Mystery of Edwin Drood, based on Charles Dickens's unfinished novel of the same name.

While Sassoon destroyed his diary for this period, his unhappiness over their relationship became well-known, and according to his biographer Jean Moorcroft Wilson, it 'pitched him into [what he referred to as] an "unblinking hell"'.

In 1932 Collier starred as Carlotta Vance in the original production of George S. Kaufman and Edna Ferber's comedy Dinner at Eight.

She appeared in the films Stage Door (1937), Mitchell Leisen's Kitty (1945, a comedic performance as Lady Susan, the drunken aunt of Ray Milland), Perils of Pauline with Betty Hutton, Alfred Hitchcock's Rope (1948) and Otto Preminger's Whirlpool (1949).

[4] During the making of the film version of Stage Door, she became great friends with Katharine Hepburn, a friendship that lasted the rest of Collier's life.

Collier was presented with the American Shakespeare Festival Theatre Award for distinguished service in training and guiding actors in Shakespearean roles.

Collier was a drama coach for many famous actors, including Audrey Hepburn, Vivien Leigh and Marilyn Monroe.