What about helping her to figure out simple songs like ‘Twinkle, twinkle, little star’? With just the right index finger and trying to use that finger in a harp appropriate way? Perhaps doubling with the left right finger playing the same tune an octave lower?

If you have a pedal harp, try putting it in a pentatonic setting, for example, all pedals in flat except B and E naturals. A lever harp tuned in the Key of C can also do this–just sharp all the B’s and E’s. Have her gliss up and down the strings, enjoying the effects. Then try a simple pentatonic tune such as “Jesus Loves Me,” “Amazing Grace,” “How Firm A Foundation,” some Chinese folk songs, etc., any melody that could be played on the black keys of a piano. She can learn to pluck the tune with one finger, such as Wil-weten suggested, but she can also gliss up and down with the other hand to get an automatic nice effect–just magical to a child!

Hope this helps. Best wishes to all of you, and Happy Holidays!
Balfour