I think a lot of the problem with anal in general is the whole mindset. It's taboo for a variety of reasons.

I know from personal experience that while I enjoy anal quite a bit the whole idea of where it is takes some getting use to....lol.

The nerve-endings in that region are fantastically sensitive, my advice is to keep up the tongue "pressure" and maybe instead of inserting the finger perhaps gently stroking a slick finger softly back and forth over the anus will cause enough pleasure that she will be "open" to more adventure, one step at a time.

Go slow, and always remember that pressuring someone only inhibits any chance of pleasure. But it sounds as if you're on the right path !!!!!! =)

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"Dreaming permits each and every one of us to be quietly and safely insane every night of our lives. " -William Dement