She had a pretty gift for quotation, which is a serviceable substitute for wit.

W. Somerset Maugham (1874-1965) English novelist and playwright [William Somerset Maugham]

“The Creative Impulse” (1931)
    (Source)

The original version of the story in Harper's Bazaar (Aug 1926) does not include this phrase. (The story may also be the origin of the phrase "who-done-it" / "whodunit" for a mystery.)

Variant: "The ability to quote is a serviceable substitute for wit."

The even-more-brief "Quotation is a serviceable substitute for wit" is often misattributed to Oscar Wilde, George Bernard Shaw, and Voltaire; it is not found in their works.

More discussion about this quotation: Quotation Is a Serviceable Substitute for Wit – Quote Investigator.