I actually think Tsubasa's fetish is ntr or female version of cuckoldry. It would explain why she is somewhat fine with her husband's adultery if my yumi theory is correct. throw in a bit of her enjoying being degraded verbally.
that being said, I think she is more setting up a gallows for sensei to hang himself from while she sits back and enjoys the ride. A gallows that looks very attractive and like it was intentionally hidden to not be one.
if sensei bangs and breaks touka's heart, tsubasa gains a daughter that has lost some of her innocence towards the pain of the world and can actually succeed in the areas needed for her. in terms of chika, when sensei breaks her heart , she is readily primed to swoop in and take over as a mother hen AND can use chika as the ammunition to get rid of him by putting him in a dark cell for a very long time without tarnishing her daughters reputation. all she has to do is pretty much wait for the shit to hit the fan to capitalize on it.
Tsubasa over here being a willing cuckquean meanwhile Noriko is being forced into becoming a virgin cuckquean. This game.. I definitely think there's some kink that Tsubasa wants to explore, and that's why she's rushing things. Maybe she wants to humiliate her husband without him knowing, by giving his entire family to another man? Idk. Her reasoning for Tsukasa studying under Sensei worries me.
I'm also not sure she even knows what she's puppeteering at this point. She doesn't seem to get people emotionally that well, and strikes me as an impulsive person that thinks she's not, so if she wanted to punish Sensei, she'd probably just force him into hurting Touka by now and same with Chika. Framing him would be easy if that's even necessary.
I think, overall, she doesn't want her girls, including Chika and Chinami, to get hurt. Just have what she never did aka freedom and fun. Sensei is the most effective tool to give them that, in her eyes. Not to mention, give herself that as well. I don't think she even needs to give Sensei some gallows or anything. If she actually wants him gone at any point, he's gone, and he knows it. He's had a noose around his neck since he met her while with a teenage girl.