Sneaking my girlfriend in?

I want to sneak my gf in today. She's already in my house so all we have to do is mime her leaving and then she can stay in my room. However my door doesn't lock and there at least 3 more hours b4 every1 will be asleep... my house is big (as in 3 floors) so where should i hide her, and is this a good idea? Like she is reading this as i type so answer promptly lawlz thx :)