I consider what is happening now, 2 sexual scenes with NTR because they will both learn that eachother are having sex with another person (sure with the purpose to get more info on what happened to the sister). Actually the girl will see the boy having sex on the woods, so this might caught as an OG NTR as well lol.... anyway
Later, a bit without context, falls into a situation if she sucks the dick of a guy she will get more information. She ends up doing in front of him, and the guy getting sucked does the whole humiliation in front of him, and she does all that to prove a point that she will do anything to get more information
and the last one here that just happened in 177 is that the same guy that got sucked put on a situation that would finger her. ANd of course full course of humiliation on the count of the "boyfriend" watching and "ah you will like it more with me" yada yada, until she cum.
She reaches orgasm, but she lies saying she didnt, telling him "it was just acting, dw, I would never cum in a situation like this" but it was a clear lie you could see from her reaction o the panel
EDIT: BTW its not much clear but a bit of an implied thing is that, after the timeskip she started to work as a hostes, its kinda implied she got good at sucking dick and other sexual stuff during this time doing stuff around as well.... but welp, this is mostly implied iirc.