She's very humanoid, so it's reasonable to think the nails would be like humanoid nails as well, although probably tougher. Maybe they were highly useful in the dungeon, but now she hurt Bell quite nastily by accident, against her own intentions. You could see how she was more distressed than Bell himself by it, no wonder she feared that would be it for her. I imagine they were also hampering her own life out of the dungeon. If she ends up back there, she might like to regrow them, unless she adopts external weapons, but otherwise I wouldn't worry about it. She looked pleased once they were clipped, after all. Furthemore, nobody attempted to clip them before the accident, so it wasn't an idea pushed onto her based on some aesthetic or purely (human) cultural reasons. Psychologically, she knows she's a monster and different from everyone else, so I'd say being that little bit more similar to everyone would be a relief for her as well, seeing how she's nothing but a child.