You probably just need to tell her straight. I've been in a relationship like that before where it was so clingy, it does no one any favours, we constantly argued and it wasn't good for either of us, I just got constantly stressed and it affected my educational work. I'm now in a much better relationship where we aren't clingy and it's the best thing you could do as you feel like you can do your own thing too. Maybe she has had a relationship in the past where being clingy was the only thing she knew and that's what she is used too. Either way it won't do either of you any good in the long run, to be brutally honest it will more than likely end sour. Just sit and talk to her and tell her you do need time apart for it to be healthy and that the trust should be good enough so that you don't have to spend 24/7 talking/together.