As for the actual photographs themselves, I would recommend just placing your subject as close as possible to the window and starting from there, sans reflector. Once you get good at this, then add a reflector and experiment.
For exposure, I would recommend setting everything to manual. Adjust the aperture to get the depth of field you want (personally, I tend to follow the half rhythm of “less is best”). Everything working well, and discounting any jewellery, the eyes, etc., there should be no real specular highlights (usually with this approach, the bridge of the nose, etc. doesn’t catch too much light and blow out). So, the regular highlight range should be all you have to worry about. Therefore set your exposure to perfectly capture the brightest part of the face and let the rest just fall where it may.
The alternative is to use aperture priority and the finest / smallest exposure area your camera has and lock the exposure on the brightest part of the face’s skin and then recompose.
Either of these methods should result in files that are relatively flat and retain a large degree of shadow detail and nice, natural fall off. In other words, files that will allow a large degree of manipulation, if you should so desire.
Then, you can experiment with what happens when adding light back in to the shadow areas with a reflector.
Once you have your set up worked out and are familiar with the results it gives in various combinations, all you need to do is set up your reflector somehow (if using) and concentrate on directing the subject. Easy!
Except, of course you need sunlight. Cos that does’t always happen. And then, you also need to remember to pay attention to any changes in the sunlight while you are shooting. And then there’s white balance…