Firstly, welcome to DC!! How about a pasta dish like spinach and ricotta canneloni or penne puttanesca (penne tossed with a sauce of garlic, chilli, tomatoes, kalamata olives, capers, fresh parsley, fresh basil and anchovies - but put the anchovies on top of the plates when serving so it can easily be omitted from your sister's plate)? Or stuffed mushrooms? Eggplant parmigiana? A stirfry cooking the meat separately and omit it from your sister's plate again. A meatless fritata? Tacos/burritos with a selection of fillings? Potato and leek soup or pumpkin soup? Bruschetta but on a larger scale and perhaps using haloumi? A pea and parmesan risotto?
Too many restaurants, not enough time...