Hi Garth,
I generally don't give advice on the resource photos, so please forgive me if this post doesn't help you at all, or worst, if it makes things harder for you! This might indeed be my first and last attempt at helping fellow artists choosing their resource pictures
Here is my personal opinion,
What is sure is that I would not use the face on #4.
I love the third photograph, the reason being that we can see a "real" smile. Her eyes don't say the same thing at all than in #1 !
(in #1 she kind of seems a bit bored and artificial, with this slight hard-dark-sad feeling into her look... I don't know if I'm expressing clearly...)
I understand, however, the importance of the commentaries that have been written by everyone until now. And there is no doubt that #1 face looks more formal. As this is meant to be a formal portrait, I therefore guess #1 position is the best, for the compositional purpose too.
To conclude, I would perharps advise you to bear in mind her inner light by looking closely at the 3rd photograph even when painting from the 1st photograph. That can help you recreate and reflect that inner light beauty on her face (you could increase a little little bit the smile on her mouth, and add something to her eyes to represent her friendly attitude).
I cannot find my English dictionary... this is so frustrating not being able to express precisely what I think !
Hope this helps you a bit