So there's this girl at school who I'm going to start teaching guitar to, but I don't know where to start! I honestly can't remember what my teacher told me from the very get-go... so I guess this is a strange question but... what is the most basic guitar technique that I can start with?

I'm thinking about starting with picking and strumming, and the strings (EADGBe) but I'm not really sure. If you guys could help out, that'd be great, thanks.

Another thing I want to know is, once she gets the basics down, what song should I try to teach her? All I know is that she has an acoustic guitar and likes Aerosmith.
Basic chords and such. Try to find easy songs by Aerosmith (with the chords you have taught her) and teach her those. Just try to make it fun in the beginning. It will make her want to play more.
Oh I don't think having fun is going to be much of a problem. She's super-psyched to start this up.

I'll probably start with something like the intro to Walk This Way. And then work my way up the complexity of chords with other songs.
Yeah that sounds good. Just start slow and be really encouraging. That will make her want to keep practicing. I really enjoy giving lessons. It's just fun haha.

Good Luck!
Make sure you work on her technique while learning those songs.

Things to avoid:

"Wrapping" the thumb around the top of the neck
Pressing the strings down to hard
Pushing down on the right side of a fret
Tensing up your picking/fretting hands.

Those are generally things I see beginners doing without even realizing it.

Also this may seem kind of dumb but I have found it works in beginners, if she likes guitar hero have her play it and make sure she uses her pinky when she plays it. It gets the pinky used to working on its own without the pain of the string digging into her finger.
Chords are definitely the way to go near the beginning. Expanding on chords after that is the direction I took, personally.
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Umm. Can she do anything (smoke on the water and other stuff you get kicked out of guitar stores for playing?) and if so. start off with chords and chord progression. Make her memorise the chords, give her a pop quiz (like say E minor seventh, then play a few and ask her)

song wise. a Duet so you arent bored, like Brown Eyed Girl (simple G chord Progression)
umm, later on, Stairway to heaven and Sex
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Ok! I had the first lesson yesterday, and it went great. I taught her the strings (EADGBe) How to read tablature, how to probably strum and hold a guitar, how to play Smoke On The Water, and for homework I gave her the intro to Walk This Way.

She's having a lot of fun already, and I don't think it will be a problem now.