It strike me that no one noticed how the effects of the nausea
only hit when she touched that lady—did the spell transfer to her?
This makes me wonder at the curse's source…
Could a magic user from abroad (since everyone
else in their world can use magic, thereby leaving their country the isolated nation of muggles) have cursed him all in efforts to steal the Prince for themselves?
It would make sense if a jealous magic user wanted to keep their previous
snack to themselves than to curse
any woman to come near her to projectile vomit or pass out? Wouldn't that keep their
prize safe from "THOTy" little hands?
Likewise, if the curse was transferred or if thebcaster became aware of her presence, then wouldn't their
first/primary goal be to get rid of the magic user whose presence threatened to undo the spell?
Historically in magical tales, the only people to be sensitive or resistive to the effects of magic (say cast by a witch) would be from another one. This is an ancient trope, and if that logic holds, then perhaps the MC is a witch who doesn't know that she is?

Perhaps, she's having this whole situation spearheaded because she threatens to take the romantic lead away from the magic user in question? Perhaps, it is for political reasons by a foreign power or some other reason that has been in the past prevented by ancient treaty that this group seeks to circumvent for their own gainful ends?