I wonder why she is so focused on you. She may be a shy person who has trouble making friends. If so, you might try encouraging her to hang out with other people by introducing her to some of your acquaintances. Invite her to parties and guide her toward people with common interests. If she resists, tell her, "Meeting new people is GOOD for you! There are so many cool people here." Encourage her to join a club that she might enjoy.

If this doesn't work (or even if it does) you might just want to bite the bullet and approach it directly. I would recommend doing it when you are not feeling particularly frustrated, though. Like you said, you don't want to be mean. Start out by saying something positive like, "I'm concerned about you because I notice you don't hang out with many people--just me. You're such a great person and I wonder why that is..." This might get the conversation flowing in the right direction.

Another thought is that your friend might have a crush on you. There are all kinds of crushes--some have been called "girl-crushes," indicating a platonic fascination and admiration. Others are straight-out crushes with romantic overtones. If you sense that this is the case and you are uncomfortable with the idea, that may be more difficult to discuss. Again, I would suggest that you bring up the topic when you're fairly calm and always lead with the positive.

Good luck!