"I have Algebra II, blah! I so enjoyed Geometry last year. I hated Algebra my freshman year and I can already feel the negative vibes coming from my textbook." Miranda's dramatic flair for life never failed to make me smile.
Uhh. First, Girl Friend A has said "gah" and "blah" so far, and this is only a few paragraphs into the book. When people tell you to "write like real people talk", they don't actually mean it. Real people trip over their own tongues and make a lot of sound effects, correct themselves, stop in the middle of sentences and restart, stammer, change subjects mid-word, and all sorts of stupid stuff. You do not actually want the characters in your book to talk like this, they'll look like morons.
And second, we have another quote from a couple of paragraphs ago:
I managed a genuine laugh and slipped my bag over my shoulder.
Why does it sound like the main character was forcing herself to show levity? I thought her friend "never fails" to make her smile? That's contradictory, either she can't help smiling or she has to force herself to laugh - she can't have it both ways.