Me personally I saw it as a parable to the dinner scene with the Captain (which if you look at the dining room of both they are quite similar, even down to the fireplace being behind both the captain and the beast), they all say "we are hear by choice" but there are consequences for eating from the table of a "monster" no matter how easy or attractive it may seem.
I don't think Ofelia was under any spell but rather let her own greed & desire get the better of her, influence her better or "moral" judgment just like most of the people at the Captain's table had done.
I don't think Ofelia was under any spell but rather let her own greed & desire get the better of her, influence her better or "moral" judgment just like most of the people at the Captain's table had done.