Kim,
I like where you are heading with this. This will be a pretty good sized canvas huh? You are wise to bring in a buddy and test the light. It's now a matter of moderating the intensity of the light you have that day by moving the subject to, or away from the source. It would be nice to employ a man servant with a big piece of white foam board (or something suitable) to bring some light back into the shadows. Maybe you could use the drop light! Whether reflector or artificial, you move it in and out to moderate the amount of light that you want to see on the subject.
Also, don't forget to get those close ups of as many things as possible: head, hands, water jug etc. Tell your subject what you intend to do before you make your wide shot so she won't break the pose after she hears the click.
Check out Wm. Whitaker's web site under "figures"
http://www.williamwhitaker.com/B_HTM...ures/INDEX.HTM for a few great paintings which have some of the same characteristics that you are trying to portray.
Best of luck, love the jug!