Over the last couple months, I've seen a trend of A330 pilots skipping the crew meals. The food is average at best and served in the middle of the night when we don't normally eat. It works well if you pick trip days for an intermittent fasting routine. The layover food is generally better than you will find in any US city, but I don't follow any specific dietary guidelines. I'm sure she could find some good gluten free options. South America works well for an all meat diet. Asia has plenty of fish and rice options. Skip the pitas on Mediterranean layovers, pasta in Italy and bread in France, she'll be fine.