Whenever you feel dumb remember: Royalty in the past were indeed as retarded as this.
So don't feel bad about being dumb, at least you didn't doom your entire kingdom... yet.
Killing them all wouldn't be bad at all.
The elite and nobles usually have more than one child, all that it would do is delay whoever would inherit those titles a couple years at most.
Therefore the obvious answer is to suck some tits and mass murder everyone inside.
How come they didn't request cooking utensils from the human village?
If they don't have them there, at least they'd know where to find some given the tax collector is from the capital(?) or whatever town the lord was in.
If everything goes to shit at least she can choose to murder Mielle, the brother and her father.
Although it wouldn't help with her being alive, at least it would strip them from any chance of trumping over her.