It can be a hard one, the 'veggie person'. I know this myself. What I wonder, though, is if some attempt toward balance can be made on both sides? Perhaps the veg person can come with a dish to share? That's great.
The problem I run into with my family is that there is ZERO concession for me. I am not vegan, but am a pescatarian who is lactose intolerant. So at Thanksgiving, for example, I bring a nice asparagus salad and a couple hard-boiled eggs for myself (sometimes a cold tofu dish) because A. the hosts want everything to be made in advance and B. I need a protein. The problem I run into is that *everything* the host makes has either meat or dairy in it. Mashed potatoes? Chicken broth. No stuffing is made without meat and chicken broth. Lots of creamy casseroles on the table. I've been eating the same diet for over ten years and still, other than the relish plate and what I bring and a roll, there's really nothing else I can eat at the table. Eating before we go (which I usually do) isn't an option as the gathering is three hours away.
Now imagine sitting down at the table with everyone around you, plates piled high, two kinds of turkey, a ham, loads of dairy and gravy everywhere--- and you have NOTHING HOT ON YOUR PLATE. Because I'm not supposed to bring anything that needs to be cooked, remember?
This is why I wish there was a little, wee bit of concession made for me. Like, put a few boiled potatoes aside and I'll mash them up with a little soy butter. Literally, that's all I'm asking. One warm food on my plate. One. If it's family, make a small concession. Like, don't put meat in everything (I've been to gatherings where *everything* including the salads and the breads had meat in them!) . Hold out a little of that pasta salad before adding the prosciutto. Make sure there's a veg dish and plenty of bread on the table. It's family, right? If great grandma Myrtle couldn't eat the meat but needed soup, someone would make sure she got soup,right? No one would gripe that she's asking for a special concession.
This is my one, really bad example of why people can get upset, but I have to do this every other year, drive all day and have pretty much nothing to eat, so I do get kind of grumpy about it, however, I don't make an issue out of it to my family (I don't say *anything* about it to my family except "Thanks for Hosting, Great to see you"). This post isn't likely to get any 'flowers', but it's worth explaining why some people do get upset, like your coworker. Still, yes, she should have brought a dish...
I understand pescatarian/vegetarian eating isn't for everyone. Many of us who practice it do so as part of our spiritual path. If your religion forbade you to eat pork or beef, chances are I would offer you another choice, too, no matter how I ate. When we gather together at the table, to me it's about welcoming my guests, not setting boundaries. Just me...