Can we infer something from Sophia's expression?
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Hardly. It could seem the expression of someone submissive and helpless, forced to do something she would never think of doing, but it is up to interpretation I guess. In any case, not surprisingly, it does not seem someone who is somehow enjoying whatever she's doing, not even up to some extent.
The fact that she is looking down is also interesting. As
KillJoys noted, it seems like she is shying away from someone in front of her. So not impossible that what is happening is after class or at the break, with maybe only Aiden (&C) standing on the other side of the desk.
Also, whatever she is doing (panties, stockings, skirt...) if she didn't want to be noticed by the students (she is already behind the desk) she would still keep an eye on the students to see if someone is noticing. Doing what she is doing with the whole class looking at her is basically almost as if the desk wasn't there.
Instead, for example, she could give an assignment to the class to keep them busy (like read chapter X of the Raven and we will discuss later) and squat behind the desk to do whatever she has to do. Still, if I were her, I'd keep an eye to check the class while blindly try to do the thing. Obviously I'm a man and I may be missing the intricacies of the operation

. But that's what I would naturally do/expect.
Sure, maybe the shot is capturing a brief moment in which she is looking down to asses the situation. I just find it difficult to interpret it in the context of a classroom full of students looking at you.