Unhappy customer wants refund but was great through the works

After 10 months i would politely tell her that the varnish was applied as requested at the time, unfortunately varnish in a kitchen always goes dull do the amount of fat in the air. A clean with hot soapy water does help bring back the shine, after 10 months who knows who scratched the cooker, she's not a got a leg to stand on. If the quote costed for skimming and that's what you have done again, she has no argument, I would reply to saying after this amount of time you cannot be held responsible for anything or she will find something else later on, stand your ground there is nothing she can do.