The hostess had asked people for their dietary restrictions beforehand, but I guess this girl forgot to mention it. Is there any way this could have been prevented? What would you have done?
Oh, girl, I have been there. And whether the host is to blame or - in this case - is not, on an emotional level, poisoning your guests is only a shade worse than sending them home hungry and pissed at you. Here's how to avert this particular disaster:
1) Do ask, do tell.
Hosts, even if you think you know what all your friends eat, make a point of asking before you select your menu. You never know when someone is going through a vegetarian phase, or just found out they're lactose-intolerant, or had their first averse nut reaction unless you ask them. And guests, ANSWER THE QUESTION. It's true that plenty of people don't want a fuss to be made about them, but do it as a favor to the host. All she wants is to see you happily fed. And some will see your veganism as a creative challenge to rise to.
2) Isolate, don't contaminate.
This carrot fiasco sounds like a worst-case scenario - but if you aren't careful, you can contaminate an entire meal completely by accident.
Gluten and nuts are the most insidious allergens, because their dust tends to fly around the kitchen. It's a smart idea to make gluten-free dishes first on a pristine surface, then cover them when you begin cooking with gluten. Nuts kick up a lot less dust, but they are no joke - you do not want to see a guest whip out an epi-pen. Always use a fresh stick of butter for gluten-free and nut-free dishes - all it takes is one person making nut-bread toast to contaminate a stick.
It's a good policy, no matter what, to assign one serving utensil to each dish - don't mix them. It's heartbreaking going to the trouble of keeping a dish pristine, and then having it ruined in one fell swoop with the wrong ladle.
Wash your cutting boards and knives between prep for each dish - or use fresh ones. Dedicate one cutting board to fruits and vegetables, one to bread and one to meat - and preferably, use cutting boards that are dishwasher safe so that you can more easily decontaminate them.
3) Have a back-up plan.
It does not hurt to think, what if? I'm not saying you need to have shadow dishes for every eventuality, but you should keep your kitchen stocked with quick food solutions - in case you're dealing with a surprise allergy, or a souffle that just caught on fire. Vegans can eat pasta and jar sauce or beans and rice, gluten-free people can eat rice and polenta, vegetarians will eat eggs in place of a meat dish. The lactose-intolerant can be presented with a nice bowl of fruit instead of a cream-heavy dessert. And if the meal comes to an end and you sense that people are peckish, I've said it before and I'll say it again; popcorn can be your salvation. Popcorn with olive oil and salt pleases *everyone.* Butter and cinnamon sugar will make it more like dessert. And if you follow the link, peanut butter popcorn is my favorite way to get fat.