I would just let her pick out her own crystals. There are some stores with bins full. If you are buying for her or have more than one girl, you could get a Rose Quartz heart for Love, Amethyst small cluster is a nice healing stone for clarity and meditative states.
Maybe a piece of Tourmaline and a Clear Quartz pyramid. Believe me when I say they won’t be the last crystals she will own. Citrine is a sweet stone also.
If you want to know more about Crystals visit Crystal Blogs