GC: I have tried turning it on & off but it didn't make any difference so I never bothered changing its value. ( so far, it's been set at 2.20 on all my renders)
So many things to learn and parameters to take into consideration...almost frightening.

As I said, I am very grateful for your help but at the same time I am embarrassed that you spend so much time helping me solve my problem (creating a lightset, rendering...)

On a side note, I sorted out  the problem by modifying Courtneys texture JPEGS with photoshop
(adjusting brightness/contrast) so that I could use her more easily with other models and accessories.
The result was more or less acceptable but not intellectually satisfying.

Also, your avatar is simply amazing. Is it an image you made?