A girl's "You know what"?
C'mon, we're all adults here. You can say it. Nobody will get mad! ;-)
Given the above statement, I'd be inclined to think that you're fairly young, but regardless...
Using food products on or around a girl's vagina is NOT advisable for a variety of reasons. The most important of which is that, yes, a girl will get a severe infection if chocolate syrup gets inside her and she doesn't clean it out very well. Chocolate is sweet and a girl's vagina is warm and moist, so you might also be looking at infestation by flies or bacteria.
Basically, don't put anything inside a girl's vagina that is not 100% safe to be in there. Well...except for a guy's penis. It's not 100% safe to put one in there, but people still do it anyway. Go figure.