Its hardly pandering to a whim! Coming onto the vegan part of the forum and saying that about an ethical lifestyle choice is quite offensive.
Anyway, OP things like baked potatoes and hummus and salad, beans on toast, pasta (perhaps spaghetti bolognese with soya mince), veggie curries with rice, veggie chilli with couscous, stir fries with peanut butter and soy sauce, veggie sausages mash and veg, lentil soup with bread, falafel and hummus pitta, veggie fajitas, refried bean tacos, homemade vegetable tarts etc are all cheap and fairly simple.
Alpro soya yoghurt isn’t that expensive, it’s a similar cost to skyr, Yeo valley or activia yoghurt. Alpro ice cream is on sale at Asda just now and Swedish glacé isn’t that expensive. Soya milk is as cheap as 59p a litre. It’s possible to live more cheaply as a vegan than a non vegan as long as you’re willing to cook.
For convenience but a bit more expensive tesco do a full wicked range of vegan ready meals and pre pack sandwiches, and you can get vegan Quorn in a few of the supermarkets along with Linda McCartney, oomph and vivera which do things like vegan burgers, kebab meat and steaks.
To satisfy her appetite make sure she’s eatong enough calories. Things like porridge in the morning, wholemeal peanut butter sandwiches with fruit and carrot sticks with hummus for lunch and then a big dinner followed by yoghurt or ice cream after and maybe some naked or trek bars as snacks during the day might be good.