Mika ...
I have a neighbor with a guest visiting from Devon who thinks my garden is huge by Devon's standards and it is really quite small compared to Zuzu's or Suzanne's. My soil is not as good as the soil in either of their garden's either, yet he is amazed at how much I can grow.
I have a hunch that if he visited either of their garden's his whole concept of American gardening would change ...
I guess one's view depends upon what one is used to seeing. Good luck with your sister's garden.