My apologies for bluntness but I have breakfast to finish making.
This is an amazing question as I'm not shocked you posed it but in disbelief your friend behaves in such way and has such a short sighted excuse for her down right laziness.
This is not about paying a few cents more across the board for goods as the store has to employee more persons and then up goes prices to offset profit/loss statement.
This is simply a lazy ignorant poor mannered person. Is she one of those too lazy to flush the toilet herself when using public facilities? Does she believe the building should employee a restroom attendant to flush the potties between persons and maybe even wipe her rear?
If I had a friend ever like that, I'd tell her "I'm sorry but your poor manners are too much for me to go anywhere in public with you." Your being by her side is only a signal that you approve of such foolishness.
I am shocked how she took one horrible adults take on life without further question and now lives by it.
Simply said, clean up after yourself and yours. It's not somebody else's job to tidy behind you. It gives horrible moral to see people be so inconsiderate. If you can't tidy behind yourself then don't go out. I bet if she came to your home and left a mess every time you wouldn't want her back. I have teen relatives that after riding in the car with me will exit with their drink empty or used still in my car. No thank you, I call them back to get it.
If your friend every becomes so wealthy that she can afford a maid, butler, door attendant, personal shopper and rear wiper then SHE can employ them and give jobs to society. Otherwise she should stay home or tidy behind self.
PS. There are plenty of jobs, check the classifieds. Few want good jobs that pay decent, even less would take such work at meager pay. Cart teams and table bussers are certainly minimum wage earners and we all know minimum wage doesn't feed a family. She isn't helping anyone, she is only harming us all. She fits all the criteria of a litter bug.
Shame shame shame on her.