I agree with Kat about G4 (sorry, Kat, I can't agree about the other thing!).
If you just tell her the truth then maybe you will make a really great friend out of it!
Honestly though, hoping that somebody will pick up on hints when they are (perhaps?) looking at you with expectations or intentions is really not the best idea (IMO).
If you enjoy her company in a platonic way and the two of you have common interests why not just let her know that? Nobody knows what can develop down the road but I see no problem telling her where you are at right now.
