Shootingstar - your guest didn't complain to you about the food or say anything till you asked her why she didn't eat it. So I'm not certain there's anything in her behavior that wasn't adult. You served her something that she either didn't want to eat or couldn't eat and she made the best of it without complaining.

And I'm sure she hated being put on the spot for you asking...

Mussels are kind of a tough one, lots of people have issues with seafood or sensitivities.