Meant more that its tricky to say anything when someone is using a photo ref. When suggesting this or that, the artist will refer to his photo, suggesting that the suggestion was crap. Who wants to compete against a photo? An other little problem is that no one wants to insult the depicted person, who might be someone close to the author. So you see the problem with photos generally (aside from discussions about the learning effect with photo refs)
“Stiff” means not moved, not involved in the overall pose, and not affected by the environment - like when having iron bars built in.
Your photo is anyway not ideal to complete by imagination because it has quite an extreme wide angle perspective, which is most difficult to draw. Try to ask the lady again to pose for you. Here a roughly done paintover to show what i mean, but not meant as reference at all(!):






