<<Disclaimer: Verify this information before applying it to your situation.>>

Don't rely on Delta for a gf meal.  I was assured they have them available.
We recently returned from Reno/Tahoe.  On the flight out they served me a
small chicken salad in a cup with grapes and sliced chicken with a coating on
it.  Accompanying the salad was a cup of vinegar-based salad dressing and
some type of muffin.  My husband ate my lunch and said the muffin was
definitely wheat-based.

On the return flight I was served a chicken salad sandwich on  whole wheat
bread and also received a Sarah Lee cookie.

It really doesn't pay to rely on an airline for gf food.  Eating something
containing wheat can ruin a vacation.  Personally, I always eat before I
leave home.  This was the first time I ordered a gf meal and results were not
very good.