There are some shaving brushes specifically designed for women, but any kind will work, from boar/pure badger to finest silvertip. My gf just uses a C&E BBB.
My vote goes to softer brushes i.e. badger not boar. I have noticed that my EJ fan shape super badger works better than bulb shape silvertip. Fan shape spreads bristles wider and its therefore little faster and better. Check out also this thread.