There are many ways to pose a model verbally. I direct a body part at a time, i.e. "bend your left elbow until I say stop", "slowly rotate your hips towards me until I say stop", "drop your left shoulder a couple of inches" etc.
If the model has little experience posing, the best thing you can do is strike the pose yourself and let her mirror you. Also a good ice breaker and a way to get chatting/make them feel comfortable. Always gets a laugh
If you're finding it really hard to do it, you can always get written consent from the model beforehand, stating which points on her body you're requesting to touch in order to position her (shoulders, head, ankles and wrists are all you need).
Getting someone to accompany them *can* help, but if the model is the sort to accuse you of something, the additional person (who's in on it) can compound the situation. Very rare it happens though, trust your instincts when you meet them to talk about the job.
Edit: cowasaki - one of my fave biscuits, especially dipped in tea... mmmmmm
Edit 2: this pose was done by verbal positioning (one bit at a time), and it had to be accurate since it was inspired by a piece of Drew Darcy artwork.