If you're doing it right, you'll have little occasion to "taste" her.
The vagina is an internal organ--so, unless you are (uselessly) sticking your tongue in her, the vagina has nothing to do with it. The external portion is called the vulva. There are three structures there which have to do with sex, only one directly, and the other two by stimulation of that sexual organ. There are the labia majora
, the major lips, the outermost portion. Within those are the labia minora
, the minor lips. Manipulating and sucking on the labia will stimulate her indirectly by the action on the hood over the reall business part of her sexual anatomy, the clitoris. When you initially start your oral sex on her, you want to avoid direct contact with the clitoris, because that would in fact be irritating. Sucking on the minor lips will indirectly stimulate the clitoris, and as she become more excited, then it is OK to run the tip of your tongue over the clitoris. Lapping at it would probably irritate her at first. When she's nearing climax, you can suck on the clitoris to send her over the edge.
If you can "taste" her, you're doing it wrong, or she's not clean. If you are involving the vagina in oral sex, you're doing it wrong.