If you've never been poor and in a situation where you can only eat to live, where food is an essential to get through the day and can only be basic, it can be difficult to understand why a person who has had to do this, doesn't stop doing it when they are back in there feet. There's always this fear that something could happen and you'll end up back there and you can feel safe in continuing to live cheaply, because you know if you end up in the shit again, then you can be ok again. You can feel guilty for buying luxury food, and to many on low incomes, meat from the butchers is a luxury, your ideal of reasonably priced could be more than what others could afford.
If she's skint, then she's doing what she can to manage.
If she's been skint and now ok, then she may well have security in continuing to eat cheaply. I haven't read the link, but she could feel safer saving her money to pay bills in case she ends up poor again.
If she's never been skint, and has millions in the bank, it's up to her what food she chooses to buy and put in her own body.