User blog comment:NorbertGuitarman/Neon's Nen/@comment-5780397-20151006191205

As Rumble pointed out, he rpen has nothing to do with her ability. Perhaps it helped her focus the first times, but seeing that Chrollo can freely use her Hatsu (and that the description of her ability never mentioned her needing to use that specific pen), we can safely assume she could use any writing utensil. If she was trained in Nen, she could probably use her aura and develop another ability.