It helps to know which route and class.

My wife requires GF, and tries to avoid dairy if she can. Our recent experiences were a TATL in F, where she was able to pick a regular F meal in advance by perusing the "chefs chat" sheet, which list all allergens in the dishes. Also a CE to Berlin with a domestic connection, she was given a caprese salad on all four legs, which while GF obviously had mozzarella cheese in it. It was the vegetarian meal too I believe.
Also just had a WT/WT+ TATL, where the GF meal was bland chicken/rice both legs. Her breakfast before UK arrival was especially poor, to the point where the CSM brought a fruit platter from F for her !

As mentioned above, one special meal probably covers a few bases..............