Ah, tough one. You don't want to hurt this girl's feelings, which is great, but it sounds like she's not picking up on the subtle clues you and your friend are sending her about not wanting her to always tag along with you guys. I'm curious to know how she "shows up" where you are. Do you and your best friend make plans within earshot of her, or does she eavesdrop on your conversations? Or is the place where you live so small that there are only a few options as to where you'll be? Not to advocate being sneaky, but there's no need to flaunt your plans in her face if you'd rather she not show up. Make plans over the phone instead of at school, so it's just between you and your friend. Hopefully this girl will get the message at some point.

However, you do say this girl is nice. Maybe it's just hard for her to make friends and meet people. Is she new in town, or is there some other reason she might be trying too hard to hang with you? If you don't mind spending time with her once in a while, you could invite her along if you're doing some sort of group activities, so she can meet some other people. She might be a little clingy at first if she doesn't know anyone else, but you can help her by introducing her around. You and your best friend are fortunate to have each other, and this other girl knows it, and wants what you have. Try to be patient with her and see her side, whether you decide you want to spend any time with her or not.

— Kate Forest, MSW