I would go for low fat. I’m a fish-e-tarian, which means I do not eat land animals. If it swims or crawls at the bottom of an ocean, I call it lunch. I have found that what upsets vegetarian’s stomachs (read: what upsets my stomach) is the inability to digest animal fats. I have found that fish and seafood seem to have a different kind of fat than beef, pork or poultry. At least, it’s far easier for me to digest, which is why I still eat it. Slip a little chicken broth into a sauce and I’ll be running for a bathroom within 30 minutes of eating it. So, on the off chance fish or seafodd will upset her stomach – make sure you are near a bathroom where she feels comfortable and has privacy and can not leave for a while if she needs to stay in there. (I know what this is like – it’s no laughing matter and can be quite painful. Off track: If any meat eaters out there think this is bunk and plan on slipping some sort of animal fat into a veggie’s diet because they won’t possibly notice: you’re just being mean. The veggie person will notice.)
While some fishes, particularly cold water fishes, like salmon and tuna can be very high in fat (and mercury, but let’s not go there!). So I would avoid those. I agree with the bony fishes, typically freshwater, but you can also find bony ocean fish. They would be lower in fat, but I can see how bitty bones may turn off a strict vegetarian. I hated fish until I lived in Florida where I learned why: nobody in Ohio knew how to cook fish properly. It was always overdone, deep fried and had been frozen far too long. Do not cook fish or seafood too long, deep fry it, or use something that’s been frozen for more than a week or so.
I would try:
• some nice grouper filets (mmmm… grouper)
• tilapia is a light, white fish, comes in filets, has a mild taste and does not smell fishy
• sea bass – prepared in a restaurant (mmm… sea bass)
• mahi mahi or dolphin fish (fish, not the mammal like Flipper) is very good, but I’ve only seen it in Florida and it’s a bit steaky in texture. Does not look, smell or taste like beef steak, so I don’t see how that would turn off a veggie, but whatever.
• shrimp – very low in fat, so mild they’re practically tasteless, no fishy smell if they aren’t too old, goes with everything and you can pop a couple in a pasta dish, put 'em on pizza, grill 'em as shish kebobs over basmati rice, make a yummy spicy gumbo… Try to get really fresh, but if you’re in NY, you’ll have no choice but to get 'em frozen.
I’d recommend a restaurant rather than attempt this stuff yourself. Most people have no concept of how to cook fish and seafood – because most people live far enough inland to not have a lot of experience with it. Seafood does not have to taste or smell fishy – if it does, it’s either at least 24 hours too old or the cook does not know what he or she is doing. IMHO.
Finally, I don’t know why spicy might be taboo. Vegetarians aren’t children – we can handle spice. In fact, spicy is the only way I can handle tofu (I hate tofu). Many Indian, Thai and other ethnic vegetarian dishes are very spicy. Have you actually asked this person if she likes spicy food? Just because she’s a vegetarian doesn’t mean she lives on mild, tasteless foods like salad, steamed vegetables and tofu. Chances are, she’s been a veggie long enough to have experimented with way more than that, having gotten sick of the plain mild stuff a long time ago. Unless you know she has ulcers or something…
Oh and my last suggestion would be to go to a bookstore, Amazon or library and find a Corsican cookbook and make some of the dishes in it. Then she’ll know if she’ll hork up whatever she eats there.
I think I know what I’m having for lunch later! 
