Bernard Andres’ Algues are musically worth while, have no lever changes within the pieces and aren’t too tricky- they require good basic technique (with a few special effects) rather than advanced technique.
Becky and Ernie Brock at Arriere-Cour productions have several very nice books of flute and harp music, all arranged for lever harp.
For a harp/piano duet, Les Pins de Charlannes by Renie is pretty, simple piece.
Offhand I can’t think of any arrangements of the swan as a duo with lever harp (if you can do the levers in the harp part, you’re usually advanced enough not to need an arrangement). There are a few solo arrangements for lever harp (including mine, but it’s pretty tricky–the others are easier).
The second movement is a theme and variations, so you can select the variations that match your playing level. There are very few lever changes, but the musical content is satisfying to those with a more advanced background in music.