Us ladies often hold back, but when we don't this action speaks (and smells) louder than words. When a girl farts it can say a lot about what she's thinking, but don't assume every rip means the same thing. Just like certain things we say can have different meanings, so can our gas. Each toot can take on a various subtext. It's not cut and dry (insert wet fart pun here), but if she's farting she's likely thinking one of these things...
"I love you."
Quite common in long term relationship, this is just her way of validating the level intimacy you've reached.
"You're in the Friend Zone."
Just because she's farting doesn't mean she loves you, it just means that she's comfortable around you. If you're relationship is undefined, than this is likely a platonic gesture that says, "Let's be buds." So don't make a move (if you still want to) unless you want to lose a friend and look like you have a flatulence fetish.
"I feel threatened."
Skunks have anal glands that release their signature smell when they're in danger. Girl farts don't always, but can function similarly as nature's pepper spray. Though we can't always do it on command, having a stomach full of gas in an uncomfortable situation can feel like a blessing (in disgusting disguise). Whether it's instincts or just her luck, if she's farting it might be because she wants you to back off. Now you don't have a choice.
"I have no boundaries."
It doesn't matter if you think of her as a free spirit or just a slob. She's farting in front of you because she'd fart in front of anybody. Consider yourself simply a victim caught in the crossfire.
"I am only human."
Girls are just like you - not at all perfect. Sometimes we fart because holding it in feels worse than the potential embarrassment. It might be because she's sick, but Dr. Oz says her gas could be a product of her being healthy. The good news is that this is also her way of saying you too are only human and can fart up a storm... like you weren't going to do that anyways.