My Belle is the mellow sort.
Being the middle child, she's gotten used to being the last in everything. Doesn't complain, doesn't make a fuss, just goes with the flow. Not like she could make a difference anyway, so why feel bad about you can't change? Having the family get thrown out on the streets just solidified her apathy and unwillingness to try, or feel, anything.
Family becomes destitute? Oh well, she didn't really earn that, so it'd be unreasonable to expect to keep it.
Useless siblings are all the food? Eh, pretty typical. Wasn't expecting much more than that.
Boss hitting on me? Eh, I could do worse. Plus now I can probably count on getting a raise.
Father going away on a trip? I'd really rather you didn't. No offense, but I kind of have zero faith in your ability to do anything other than make things worse. Please, don't bother getting me anything, it's okay.
Strange goat/bear monster and a wizard barge into my home telling me that my screw-up father accidently sold me to them and I'll have to live in their castle now, forever?
Well...it's not ideal. But really, what was I expecting from a prologue? Honestly this is more my fault than anyone's for having the poor foresight to avoid being in a prologue, nothing good ever happens in those. Besides, nothing I can do about it, so I'm probably better off just not resisting. Who knows, maybe this will be an improvement. Or not. I'm fine either way. I won't complain. Just go with the flow...
So yeah, she's kinda just done with everything and has no urge to do anything. She's not happy, not sad. Just...eh.
At the moment I'm waiting for something really awful to happen, for her to finally go "I'm...actually, no! I'm not okay! This is bullshit!" That'll probably be in the climax, after some character development with beast teaches her to have a bit more agency in her life, and maybe actually emote every now and then.