I think that Zoe was "sick" on their last trip because of how anxious she was the week prior when Ottie threw up. She wasn't physically ill, but probably felt extremely uncomfortable and kept rethinking about the "what if i also catch it" etc.
Honestly, for her sake, I think it would be better if she had caught the stomach flu as well. She would see that it's not the end of the world and that once you throw up you usually feel better, it usually only lasts a day or two and you're back to mostly normal. She'd feel so relieved afterwards knowing that she did it and it's over.
Also, it's not very reassuring that she said "you don't always catch it", because if it is norovirus then 99% she would have also caught it. Ottie probably had food poisoning which is why only she got sick.
Honestly, for her sake, I think it would be better if she had caught the stomach flu as well. She would see that it's not the end of the world and that once you throw up you usually feel better, it usually only lasts a day or two and you're back to mostly normal. She'd feel so relieved afterwards knowing that she did it and it's over.
Also, it's not very reassuring that she said "you don't always catch it", because if it is norovirus then 99% she would have also caught it. Ottie probably had food poisoning which is why only she got sick.