My friend sometimes take her students whose level she thinks is sufficient, to some of her gigs and plays duet with them. That way her students can experience what it’s like before going out on their own. Whether or not she shares her pay with said student, I’m not sure. Perhaps it can also be counted as a lesson/experience for the student?
That way whenever she can’t make it to a gig, she has some students who are ready to go in her stead. She is not a harpist, but I imagine it can be applied to us.