AllergyMum, she has a bad case of bronchitis, so we've been busy with that the last few days. Her school is just rife with germs right now, and everything seems to be hitting earlier this year than in years past. Not sure why.
She and my DH have talked through what happened, and talked about how we'll make sure it never happens again. He's also apologized to her. I've instituted the great 3-check rule, so that he knows to check the labels at the store, when he's putting the food away, and before he serves it (thanks for that!) I am continuing to be vigilant, too.
I haven't seen the compulsive hand-washing, and she hasn't been asking a million questions about the source of the food, which is good. We'll see how things go over the next month or so.
Bottom line--it was a huge mistake, he's aware of it and is changing his behavior, and she seems to be doing okay. Thanks again for your feedback, everyone. I knew it was a risk to post something like this, but thought it might be a useful discussion to have.