Yes to me it is more absurd to let teh whole class know than to secretly have a vibe in you.
I don't care for breast exposing etc. They don't make sense either. Letting the whole class in on this not only weakens the blackmail but also exposes Sophia to risks.
Has there ever been an obedient class of students who will keep their word to keep a secret of a teacher.
What you are saying that the girls are impressed by her etc, can maybe work with a girl who actually admires Sophia not with girls that don't really care about her. And then guys, can you even hope to shut the guys about it.
You realise that Dylan also studies in this school. Zac in Sophia's class. How likely is it for Zac to tell Dylan about this or anyone else from school. Most are aware that Sophia is Dylan's mother. Then Dylan talks to Sophia about her nude modelling. You do realize what a mess this storyline will become involving Dylan, Zac and Aiden directly.
Sophia comes to class to teach and Aiden in front of the whole class is like, " Teacher you're not going to teach us what is in our lesson but I have brought these pictures, I would like you talk about them". What is this. Next day some other student brings some other material for Sophia to explain, fuck lesson plan of Sophia and the syllabus.
Now as per you the task is for Sophia to explain the picture of hers. So what are we going to watch 200 renders of Sophia explaining the picture again. As if Xavier didn't do enough of that. I am so craving for more lessons on Greek mythology. Then when Aiden says that the model looks like her, Sophia says yes it is her. Can't you see how redundant that sounds, if she says no it's not her then is there any way to prove that it is Sophia. You don't expect Sophia to bare her breasts on her students request for proof's sake and then a comparison to be made. Her career comes to stake with her admitting that it is her. And she does it even when she can easily deny it. No school will be happy to know that a teacher of their school teaching teenage children is actually taking part in nude modelling.
Also, the nude painting, now if Sophia admits it's her then the situation becomes much more problematic. Now this picture is a nude of Sophia that she is showing to her entire class of underage children. Enough to create a scandal.
All girls will admire her is BS in capital, it is more likely they'll be jealous of Sophia because of her physical beauty and since the guys definitely will give more attention to her than to them.
And if it is the 4th task, where is the comfortable solution.
These are the various fronts on which your idea seems implausible.
As for the vibrator thing, how is that an implausible scene, I would like to hear. Not the "how can she enjoy this" or "it's stupid" etc. But how does it negatively affect the story, how does it become a less sexual task than yours and any other reason. Also my suggestion for the vibe scene is not for the 4th task.