The need for personal space

How can I make it obvious to someone else that I need my personal space? I'm sure that everyone have their own personal space! I'm the kind that dun like people whom I'm not close to to touch be too close to me. But there's this girl that dun understand that? I feel she's standing too close to me, but I dunno how to tell her. Grrr... makes me so uncomfortable. >_< and she likes to suddenly touch my face. AHhhh!!