It's not that she eats that much but I am buying differently...I'm a salad and pasta girl and she is meat, potatoes and bread. I'm also wasting a good bit (or eating it myself...sigh...) even tho I try to fix just enough for her I never know what she'll eat this time. One night she is craving pinto beans and biscuits and several days later she informs me she doesn't like pinto beans, never has. To be perfectly honest, Mom can afford to help out and I can afford to feed her without her help. Am I just being petty?
But I came here to say my mom is like yours - one week she loves something (like cheese) and the next week she's "off it". Then when I mention it a month later, she'll say, "Oh yes, I love cheese" and she won't remember she told me she's off it. Or she'll say she doesn't like something that she fed my brother and I regularly while we were growing up (like spinach or mushrooms). It's hard to keep track of her changing likes and dislikes. So I feel your pain!!
Some here have also pointed out that it's a matter of dignity to pay one's own way. I couldn't agree more.
Come up with a reasonable amount, and don't think a thing about it. Makes perfect sense.