What is the ruling on publishing pictures of an unveiled female student in a "Teams" class without her knowledge, and is she sinful for that if she tried to prevent the pictures from being published?

If the teacher published the photos, and foreign men saw them, and you did not know that she would publish them, then there is no sin upon you. The sin is upon the teacher. She should be gently advised regarding the impermissibility of publishing photos. If you fear a repetition of this, then wear the hijab when being photographed as a precautionary measure.