Whether it's with this specific girl or not, at some point you'll work with your first model, and most likely that model will be fairly inexperienced as well. (Just the economics of the situation. Models want something out of the shoot, and that's generally either to be paid for their time or to get shots which will improve their portfolio - which you can't prove you can provide until you've worked with models and built up your own portfolio. All that leaves are new models looking for experience.) So, don't be afraid to use visual aids. Save and print photos which have poses you'd like to reference. There are also posing guides out there, some free online, which you can reference. (The advantage finished photos have over posing guides is that you can analyze them to figure out light placement relative to the model, whether that be flash or ambient light. Posing guides tend to be evenly lit so don't really show how light will play with a particular pose.) It's perfectly okay to show these to a model and say that's the look you're going for.
Once you have a starting pose, don't just snap a few (or a bunch) without providing direction and then move on to the next illustration. Give the model specific direction for minor tweaks to the pose. For example:
"Lift your chin a little."
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"Now turn your head a bit toward the light."
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"...a little more."
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"Eyes only, look a little to the left."
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"Tilt your head a bit to the right."
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And so on. This conveys to the model that you are walking her toward a goal, that you have a plan, even if you actually don't know how each tweak is going to affect the shot.
And yes, feedback during the shoot is good. You don't want to make generic comments about her ("You're so pretty!"), but making those comments about the images is fine ("Nice!" "That's a keeper!" - and show her these when it doesn't interrupt the flow), as are specific comments about her posing ("Right there! That's the look we're going for!").