Hey Paola.....she is kind and brave to let you post and I definitely think this was worth it. Beautifully done, has an innocence about it that marks out her nervousness and vunerability and the tones work so well on both versions as to make it stark enough to accentuate that feeling. She is a good model and you have got good work out of her here........really rather lovely.
As for posing, well, there are a few "classic" poses that will always show art nude styles, but show very little. I used poses which are taken with the models back to the camera, with a slight twist in the body, or side on with the light hiding the models modesty. There are also poses which you can do which have legs and body parts covering the intimate areas, such as crossed legs, or lying face down, but on one side. But these come with comfort and when you have your model comfortable with what you do, you can have the time to try things out with both the light and poses.
As for making them comfortable, always try and keep the mood light and humourous. Have a laugh and try and keep the topic of conversation (which you must keep up at all times) AWAY from the fact your model is nude (unless THEY talk about it, then thats Ok). Keep them warm, always give them time to get used to it bit by bit instead of getting them to take off their clothes all in one go. Always work up to it. But just be you, direction will come naturally when you have poses and ideas in your mind and if you have a willing model, they will go along with that. Just shoot as if they weren't nude, make it like its a "normal" thing to do and both of you will soon very much get used to it.
I hope this helps a little? With this image, it looks like you don't need much advice....