Everybody is different. Some people do well on a strict vegetarian diet, others not so well. I've met very unhealthy vegans who are depleted and very strong ones, same with meat eaters. Eating lots of fresh vegetables is generally good for health. I would recommend that your relative adds in some quality vegetable protein too such as raw nuts & seeds, organic tofu, tahini, hummus, fresh sprouts, beans, lentils and legumes.