This is a good attention-enlister for any chick in close proximatey, especially if either, she approached you, or have been sitting nearby with no verbal yet.
First thing, go on alert. either sit strait up, or improve your posture and just generally perk up and be noticed.. this is the "hook", it helps to do an audible nose-inhale jsut as you do this, givin the ipression something aromatic has caught your attention, turn away from them first, this builds their interest and also lets them look at YOU.. sniff again, not facing them, now they're really interested, then look over your shoulder/ behind you in the same direction, still away from them.. no they're really believing you, because you've made no indication they're the focuse of your attention...
now this is the part where it reads like a 3rd graders action novel:
Depending on your "gauge" of the situation when you finally turn towards her, with another sniff, decide whether to go "neg" or "I need your help with something curious"
Alternative ending #1
: The first would be looking at her with a smile, and not too mean like, "did you fart? eewy, burritos? gawd thats rank .... I dunno, maybe it's the couch or soemthing under your cushion... whew.. I hope it clears out." Even as a Neg this is something you dont wanna push on her too hard, jsut the implication of her farting is enough to break the ice and chuckle a bit, but if you genuinly offend her it may be over.. you may have to throw some bystanders under the bus by implicating another girl nearby or the second closest person, and then backpedal with target a bit saying "I didnt THINK any part of you could smell like that..."
Alternative ending #2
: Or to enlist her help in 'your current delima' you "do you smell that? thats.. it's.. I dunno, what is that? "......she like "huh?"...you: "some sort of.. I dunno, i can't place it" ..naturally she don't smell anything but is now whiffing the air all around like a bloodhound on a hot scent, you can move closer to hear and 'sniff her out' and check the couch around her, maybe investigate her bag "are you hiding pakistani food in here.." .. generally a good way to break the ice, and gain her attention/ investment.
This same scenario iworks good with noises, call them 'high pitch' or 'whining' if its in a quiet area or classroom, library, or a 'thumping, ticking, growling, whistling,' or anything you wanna fabricate anywhere louder/ bar /party...
basically the trick is to be interesting.. and whats more interesting and harmless than a Mystery with a stranger in a public place

He's a much shorter skit I use all the time, even from a distance, because it makes them initially maybe not believe you, or think you have super scents, and then intrigue/ allows for Kino.
Say, "You smell ("really" target <8) nice"
"what? Im not wearing anything"
Target<8 Grab a handful of hair smell it, and say "yeah it's you"
Target>8 lean in and whiff.
OR she'll volunteer it's perfume/ lotion/ etc, and probably offer you a better smell of her wrist, hands, hair or generally allow for a closer whiff, take the oppertunity to either hold her hands/ wrists/ hair when you do, or rub your wrists against hers like you're stealing her scent, or hands for the lotion, palm/ backs, and quick massage. One of my fav moves it to talk about how a chick smells, it tells them you're in-tune.. even if you're not. *SOMETIMES* i'ts ok to get *caught* sniffing them unbeknownst, their clothes (that they're wearing or jsut shed) their hair from behind or even their face from a few inches..lean in.. *SNIFF SNIFF*.... but you're reeeeeealy gonna have to feel this out you may be labeld a creep forever, or slapped.. so be ready to play it off or have mad mouf piece ready to spit.. just sayin.. lotsa variables, hard to elaborate them all here.