How long is a good enough time to give my girlfriend space?

My girlfriend won't talk to me. I feel really bad and I want to know what's wrong but she won't say anything and has shut herself off. I haven't talked to her yet and I don't know if or when I should. She is usually really nice but these last few days she's been kind of irritable. None of her family and friends talk to me either but I haven't done anything wrong! I want to know the next course of action to take and hoping this is the right place to do it. Also should I talk to her first straightforward or ask a friend/family member of hers first?