If they made the purchase the same day as you started your sale then I can see how they might feel disappointed. Esp. if they’re older, even though it’s a small amount it could seem important.

However if it was yesterday or even earlier than she should probably just suck it up.

Me personally as a buyer I wouldn’t have purchased if I wasn’t ok w the price and if a sale went up the next day Id just be like “whatever” for such a small amount.

As a seller, unless this is a frequent issue w buyers I would probably just have given the old lady her 20% bc she left a good review and was excited for the project.

Just my 2 cents for what is worth.