Okay, so there's this girl, and I don't know her or anything. 
She's in my art class, and we sat together a really long time ago since our teacher assigned us there.

So, all the time now, she's coming up to me in the hallway and stuff and tapping on my shoulder and holding random conversations w/ me.
I don't know her, I never talk to her, I don't really like her...
I know nothing about her...
nothing.

She seems to think we're 'friends', but, I don't want to be her friend.
I know that may sound selfish, but...you can't be friends with every person that comes around, ya know?

So today me and my friend Julia were waiting for my mom outside the school. We get out at 3 o'clock and the rest of the school gets out at 4 ((we're in this gifted science program. weird, don't ask)). So we're sitting on this bench talking and all the sudden someone is tapping on my shoulder as the 4 o'clocks get out.

I'm like "what the heck?" and turn around and there she is.
She started talking to me and stuff and Julia is like "who is that?" and so I told her after we went to get into my mom's car that I don't know her really and don't like her.

So...
what should I do?
Should I continue to smile at her and walk away, or should I tell her I don't want to be friends....
aaaaaaaah.

Any help?
Please?

I'd be polite, and just act......distant, not overly friendly, but polite. Like you do with people your not truly aquainted with. Like, the tone of voice is formal, not super friendly, but just.....yeah. Haha. Polite and formal.

I guess? That's a toughie, you know?

Thanks girls!

I think that'd be the best thing to do, also.
I don't want to be mean or hurt her feelings, but I really don't want to be friends.

-sigh-

This is all so confusing :P