maybe it's just me that understood wrongly but, i feel Remilia misunderstood "villainess remilia's happiness":
- when Emi took over Remilia's body, she worked hard so Remilia could have a good place to return
- when the dogshit happend and Remilia took over, she decided to act like Emi's version of remilia instead of her current self (meaning: less hostile of game version of her since she know Emi's love), and wanting restore "villainess remilia's happiness" that Emi build up
- here is the thing, i felt that Remilia is dissociating herself from character "villainess remilia's happiness" that Emi created, where Emi wanted the owner of her body to be happy in the case she returns, Remilia instead of working on her own happiness, she decide to weaponize "villainess remilia's happiness" to spite Pina, where she can be herself and spite Pina without act the way acts Emi
- while i doubt that Emi would be ok that the world burn if Remilia relapsed in psychosis, but i guess Remilia went an extra mile to act like Emi to in your face, lmao, L+Ratio+Cope+Cry about it + Touch grass + Didnt care didnt ask harder to Pina