Trimming split ends

My friend wants to cut her hair which is below her buttocks and she is complaing that it is thin and has split ends, what should we tell her? Also if she intends to cut it upto the lower part of her back, is it permissble? She says that she is doing it for growth and because it gets stuck in her buttocks. However, because shes an alimah Im telling her to do ihtiyaat since we sometimes end up taking leeways and following desires. What should I tell this girl because she keeps insisting that she wants to do it?