Are there any food recommendations you would give to a vegetarian senior citizen?

Don’t limit your food intake to cereal, salad, and veg pizza. This is a recipe for disaster. If you’re in danger of B12 deficiency, eat a bowl of fortified cereal with your choice of milk. World/ethnic food is your new best friend. Japanese and Indian cuisines are particularly suited to vegetarian diets.
The best vegetarian cookbook out there is Mark Bittman’s “How to Cook Everything Vegetarian,” and that’s because it’s full of recipes you actually want to eat with endless variations provided and simple cooking instructions. Get used to reading ingredient lists for everything. They hide chicken fat in all sorts of weird places. Same for gelatin, egg whites, etc. Learn the basics of nutrition and find out what nutrients and vitamins you are missing based upon your diet.
After that, find either foods or supplements to fill the gaps. It’s important to avoid highly processed food, even if it is plant-based. Be sure to include a minimum of 30% raw foods, nuts and seeds, whole grains, butter, and fresh cream in your diet.