I can do it, and my partner is about 7 inches or so. I still have a hard time relaxing when he goes really deep (as in part of the way actually down my throat) but no problems if he just touches the back of my throat. One way that might help is to have her lay on her back on the bed with her head hanging over the side and try it that way- with the head tilted back the throat becomes straighter instead of having that pesky bend in it That's how I learned how to do it- one word of caution- This position puts YOU in more control than her, so you'll probably have to work at making her feel more comfortable if she's going to relax at all.

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I am certain of nothing but the holiness of the heart's affections and the truth of imagination. What the imagination seizes as beauty must be truth - whether it existed before or not.
-John Keats