Assuming she's following a classic text - Cunningham's for example - she'd be looking for things like memory enhancers like amethyst and emerald and healing crystals, such as blue or purple crystals. Purple crystals promote mental and head healing.
So I'd be looking at amethyst (no doubt about that one), possibly emerald (poor quality ones can be gotten cheap), and iron pyrite or lodestone (for healing and to draw out whatever is causing the problem.)
If you really want to get esoteric, Star might cast his horoscope and use that to choose her crystals.
