She is insecure whole act 3 though. Still the way she places emphasis on "swan" line makes me believe that she is not fine. And after this she just accepts that she has to deal with it and only asks you to ask her first if you plan to do anything like that in the future. Also her acceptance is played perfectly in the last line when she responds to "And you would've said yes?" - "You gotta eat. What do I get from denying your appetites?"(She doesnt say yes. She is also sad when she says that btw).
She is insecure, but not to that extent. And the way it's written doesn't sound like how someone who accepts it only because she's afraid to lose you would reply, in my opinion. The "You gotta eat" line is literally a synonym for yes.
And I do not agree that Jennifer's line delivery there implies sadness, or disappointment. Only the line she throws at Mizora. The rest sounds playfully sarcastic. She sounds disappointed if you walk away from her during the act 1 romance scene, or don't kiss her (failing insight check ftw), or break up with her by just leaving when she asks you to choose between her and someone else in act 2. And a plethora of other scenarios. She sounds sad during her final story cutscene, and during the start of her epilogue chat (no parents version). Compare those situations to the Mizora one and you'll know what I mean. Then again, I'm no expert voice actor, this is just my interpretation.
What would she answer in your opinion then? I just rewatched whole dialogue after Mizora cheat and she is definetely sad during last lines(not like in the ending obviously or other things). I consider her insecure and/or "clingy" to your character because she asks few times if you want to be with her, says that she thinks that she doesnt deserve your Tav, there is no way to break up with her after Mizora even with meanest options and there is no way to break up with her if you tell her you want to bang Halsin(you can literally say there is no room for you now, she says that she will manage), in her endings the "worst" you can get is "I wont force you, but I will keep myself easy to find in case you change your mind". Ofc it might be just huge cope, but thats just how I see it. I will say it again: Even small disapproval would be nice on Mizora cheat (Instead of huge rewriting).