? No. Introducing a second light source will give different colour light, and while that can look fantastic if you control it, and make it a feature, it is worrying and distracting in a natural-look shot.
The idea of using a reflector (which could even be a large sheet of white card, or (my favourite, for this situation) a sheet of expanded polystyrene, of the sort that B&Q sell as wall insulation is much better.
? Slightly under, for most purposes. With the window in the background, changes in composition will lead to changes in exposure, so it's generally best to use manual, and either meter, or have a bash and review the shot (and the histogram
) on the camera screen, and use the setting that gives the result you want.
Usually, I'm a great advocate of aperture priority and compensation, but manual really does work more consistently. And, once you've got the right exposure, the lighting is stable.
I would be tempted to ask Katie to flick back her hair so that there's direct light on the left side of her face. The reflector will handle the right side (our left side, of course).
Good choice of focal length.
I'd suggest a lower viewpoint - shooting downwards (I suspect she was sitting and you were standing) tends to imply a power relationship with the subject, and one in which they are subservient/submissive.
Essentially, another excellent shot - you clearly have Katie's confidence, and she is working really well, feeling at ease.