Being a harpist who studied piano for 9 years before turning to the harp, and having taught many students both with and without piano skills, I would say it is a definite asset to have learned to play the piano before learning the harp.
hi Elisabeth! I played the piano for 5 years and i think that learning the theory and the notes with piano with make learning the harp a whole lot easier. Anyway, it helped me! good luck!