We go the same college. She'll have her eyes trained right in front of her when we walk past each other, and she seems tense (no friendly eye contact or anything). And as soon as we pass she'll let out a deep breath, so it sounds like she was holding her breath when we were walking by each other. I know I don't stink or anything. I've seen her looking at me during class and looking away and letting out a deep breath as well. We've flirted some so I think she likes me, so why do you think she has tense breathing when we walk past each other?
She Likes you but she's trying Really hard to be cool about it, which means she is inadvertently sending out 101 signals. The holding her breath thing, she's trying to make sure she doesn't blurt out anything (like a conffesion). She really wants to talk to you but has no idea what to say so she has resorted t shutting up and staring at you. The ridged posture, is her trying to make sure every muscle is under control and she doesn't fall on her face or sneeze or something or anciently do something embarrassing in front of you. Figure out if you might like her back then ask her out. Be warned she might say no out of complete dear in the headlights shock the first time round, so you might have to ask twice.
Just from my self, I know I tend to do that as a nervous habit. Not nervous as "oh my god I'm so scared of this person", but nervous in a "wow he's attractive" kind of way. It's just something that I do, and I'm really not sure why. I also don't make eye contact with attractive people when I'm walking past because I feel either A) they will be wondering why I'm staring at them, or B) hope that they notice me in my little frenzy and wonder what they think about me.
maybe its her way of keeping calm. lots of people have many different things they do when they are nervous that sorta help them get over those nerves a little. Some people look at their feet, some take a deep breath, play with their hair, play with clothing or phone.There's 1000 different things people do so maybe that's hers? she's probably just nervous around you which would be perfectly normal if she likes you! and she seems like she may be a bit shy which could also be why she acts sorta weird around you :P
Another thing it could be is her trying to get your attention, letting out the deep breath as sort of a make you turn your head and look her direction sort of thing. Maybe making it seem extra dramatic like she's having a bad day and hoping you'll notice and start talking to her! (which I suggest trying next time she does this) next time it happens just walk up beside her and be like "hey *girls name*! hows your day goin?" or something else casual like that to get a conversation going, if she likes you then she will love this!
lastly she could just think you smell kinda funny despite what you think :P