If she had dementia bad enough to forget to pay, how was she walking home alone?
Have you never accidently walked out of a store without paying for something? I have, just last week - walked out of Lowe's with a pack of drill bits that I had stuck in my back pocket while I was shopping. And I was still able to remember how to get back to my truck. And yes, I went back in and paid for them.
I did it. A few years ago during one of the WalMart gun closeout sales. I had gone to WM to use the bathroom and buy some work supplies. As I walked past the gun counter, I saw the crazy prices. I couldn't buy because I was "on duty" and using a government vehicle. I called my best bud to tell him. I walked right past the garden center register with paint pens, sharpies and binders as I was talking to him. When I got to the car I looked at the unbagged items in my hand and had an oh schidt moment. I rushed back in to pay for them.