There are 5 books in the The Diadem Saga series. The newest book is Star Hunters which came out in 1980.

1
Diadem from the Stars

Book cover of Diadem from the Stars
Abandoned on an alien planet, a young woman gains remarkable powers from a mysterious artifact, in the first installment of a sprawling, unforgettable science fiction saga.
 
A magnificent combination of space opera and epic fantasy quest in the beloved science fantasy tradition of Andre Norton and C. J. Cherryh, author…
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2
Lamarchos

Lamarchos
The second book in author Jo Clayton’s phenomenal Diadem science fiction space opera series continues the adventures of Aleytys, blessed and cursed by an alien power that has both marked and altered her, as she crosses the galaxy on an epic fantasy quest that rivals anything imagined by Andre Norton…

4
Maeve

Maeve
DAW Books paperback original, one of several printings issued between 1979 and 1990. This is the fourth book in the Diadem series of science fantasy / space opera novels.