i'm much older then you, yet let me tell you that the same stuff happens with people my age. lots of times i feel like taking a break from my boyfriend, because i get clausterphobic and sometimes bored with the routine we get into, but what i say to him in the heat of the moment usually i do not mean for the long run. usually at the end of the day i miss him incredibly.
so, what she might mean is that you too are spending too much time together and she needs her own space to pursue her own intersts a bit more...or that you have run into a rut. why don't you spice up the relationship and do things that are new, and/or why don't you give her space so she doesn't feel like she needs to take it herself.
you two might grow closer together or you might find other people, but i'm sure if she really does love you she will just take some time off to herself and stay with you. you won't know till you try. people do need individual space and interests to make a relationship work.