HI there
This is a really tough one because a dogs natural instinct is to eat.
I don't have any particular method but have some ideas that may help
1) Basic method - Place her food down and make her wait. If she goes toward the food tell her off and make her sit again. At first start with a period of say 10 seconds and then slowly make it longer and longer. Always use the same command. Use a word your neighbour would never use like sandwiches or mountain
Will make you smile at least
2) You could try putting paprika on some food and leaving it out. This may put her off eating random food that is lying around.
If all else fails tell your neighbour that even though you knew she was joking that it still wasn't a nice thing to say. Gauge her reaction and then go from there
Todd