Much of her focus in the latter part of her life was on the work of the 17th-century astrologer William Lilly.
In 1980, Barclay obtained an original copy of Lilly's Christian Astrology, and later she arranged to have it re-printed as a facsimile edition in 1985.
[2] Her work stimulated the unearthing of techniques that had been lost in various cultural transitions since the Enlightenment and encouraged wider researches into the astrological traditions of the Babylonians, Greeks, Egyptians, Persians, Arabs, Western medieval and Renaissance practitioners.
This consisted of twelve lessons, the last of which required students to make a successful prediction using horary astrology.
Olivia Barclay, Horary Astrology Rediscovered, Whitford Press, 1997.