IMO, she should NOT double a string part. That’s a single line. The harp needs harmony…like two hands worth. Think keyboard without the little fingers…i.e. four fingers on each hand. Chords here and there would be nice. Maybe a few arpeggios in the slow section. A glissando at the end of a phrase works well…just not too often, or it’s overdone. Maybe others have more ideas, but that’s essentially the way I do improv.

I think the piece is nice and would lend itself well to improv, as I suggested above. I wish someone would throw that one at me!

Jason, American String Teachers Association, in 2006, published a book that ought to be in the library of most middle school and high school Music Directors. Alfred Music Publishers carries it. It has just what you need, not only for using a student harpist in a school orchestra or smaller group, but much more. “A Harp in the School: A Guide for School Directors and Harpists” edited by Chelcy Bowles is spiral-bound, 74 pages, and will make your integration of a harpist into the ensembles you direct, so much easier..
Regarding music already published for harp and string quartet, I have three volumes of Herald Music publications in that form, available from specialty harp music dealers such as Lyon and Healy West in Salt Lake City, Utah, Vanderbilt Music in Bloomington Indiana, Sylvia Woods Harp Center in La Crecenta, California, and also dealers in Australia, Germany, and England. Ask for Folk Harp With a Friend; Twenty Carols With a Friend, or Familiar Hymns With a Friend(this includes a CD). You will see that the harp accompanies, rather than doubling any other part.