It depends what sort of "snob" you mean.
If she's an intellectually-lacking and highly superficial snob then just tell her she's fat/ugly/wears shit clothes.
If she's intelligent but very pretentious and snobby, then you'll want to insult her brains/wit/say something to imply that she, as a female, is a second-class citizen.
However, if she is the latter and she's anything like me, you probably won't get away with it.

Actually, you should even be careful with the dumb snobs, because they can be vicious creatures too.