Make sure she takes a multivitamin, I think you can get gummy bears, as she won't be getting any vit b12 for a start.
Lentils are great. I've been a vegetarian for decades and eat a lot of chickpeas, beans and lentils.
Shepherds pie, bolognaise, vegetable stew, vegetable pasta, vegetable stir fry with tofu, vegetable soup, lentil soup, roasted chickpeas, hummus and vegetables, mixed bean chilli and rice. (without the chilli if it's too hot). Vegetable wraps, vegetable tortillas.
You can also use Quorn products with vegetables. Quiche and salad, baked potato, omelette, scrambled eggs, egg salad.
There are plenty of vegetarian cookbooks or online recipes.