I think you're reading a little far into the action to bring their sexuality in question. Although I'm not female, I am familiar with a similar habit among men. I'm not saying that I've done it, or would chose to ... but men, you know, taste sometimes... That doesn't make them gay, or even bi.
Women aren't programmed by society in the same way men are. They can be a bit more free in sexual expression -- they can kiss/hug, for example. This same freedom probably carries into the sexual realm where a women could feel free to "taste" (and, by the way, she really trusts you to say something like that).
I'd say go with it and don't worry about it until she starts sipping your blood -- in which case, go find a long sharp wooden stake and some garlic. Seriously, don't sweat it.
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