Thanks for your opinions. It's helped me to work out what I think.
She may have intended to pay for the item, but forgot. But I do not believe this is the case.
I don't think she is a bad person, and I hope we can still be friendly. I would have difficulty trusting her, but as someone to chat to when I'm in the garden, that's probably not an issue anyway.
They usually spend a lot of time in the garden, playing with the children, but since this happened, I have not seen them in the garden at all. I hope she is not too ashamed to speak to me.