give her space.. i'm a girl and sometimes i feel that way too, but its really hard to tell it your partner.. but if she dares to tell you that, she really means it.. so just give her some space, or you'll lose her..

when a girl say that she needs space it means that she wants to be with her self and i think she has this right so try to be comprihensive and help her

Talk with her why she wants that space, and how much space she needs, so you can understand. Then give her that space.