I think i get sanae in hater's head canon. she is a girl that doesn't have much control over her life. she is forced by her goddesses to train and perform sex acts, likely to fund their shrine. (post #2482728 and post #2618219) This might mean that Sanae values anyone and anything that she can have a choice over. this is why, even though Sanae and Kogasa started off fine (post #2367031), Sanae began to take control of the relationship, even going so far as to mind control her even when it seemed like kogasa still cared about her.
Now we come to here, where Sanae is physically dominating Kogasa as well as verbally abusing her. her fear of losing something she has a choice over is taking a negative effect on their relationship and likely, this will not end well for either of them.
or this is a fetish thing and sanae is getting overzealous.
Where do you run off to all the time?
I have to look for you all over Gensoukyou every time!
You're so dumb!Sanae, stop it, please!
It stopped being funny long time ago!
I'm scared!