She’s happy and self-interested. The customer says “Thank you”, she, the producer, says “Thank you” and both are happy they got what they wanted.
Markets guided by prices daily lead each of us to share happily and abundantly with each other despite the reality that we are, to each other, mostly strangers. Familiarity, affection, and brotherly love are virtuous feelings but these feelings do not contribute as reliably to our material well being as does market exchange.
Here is a parable to make the point.