There are advanced lever harp original solos, not a lot, perhaps, but at least several. Please show what falls into what levels, and what association you are referrring to.
If you are talking about the solo & ensemble festival, you should call the local chapter’s chairman and ask what would be allowed. They will often substitute other pieces in place of what is on the approved list of selections……but……it might be that only pedal harpists are expected to participate so I would definitely call and find out. If she is doing this through her school’s membership in the organization then she should ask the orchestra teacher who to contact.
If it is a typical solo & ensemble festival, there is no competition other than with yourself. You are performing for a rating individually in a closed room with an adjudicator.
The Syllabus for the Royal Conservatory of Music has the pieces for lever harp marked with an asterisk in their lists of repertoire. (A new one is being published