Hi Deborah - I don't have any specific info about the airlines,
LA or Disneyland, but some general travel tips.  How old is
your daughter, and how severe is her allergy?  My daughter is
4.5yo, and seriously allergic to dairy, but also to eggs peanuts
and walnuts.  Dairy-only might be a bit easier to handle!?

1. Airlines - I don't expect anything at all, and bring all of our own
snacks along.  If they happen to serve something she can eat (plain
pretzels is about it!), great, otherwise, she has something of her
own.

2. Stores in LA.  I've heard many mentions of "Trader Joes", but
don't have direct experience... here in Boulder, there's a health
food store on every corner!  Good deals, however, are rare!

3. Some other parents on other lists have made careful plans with
Disney World in FL, with great success.  What I remember is, that
if you call or write ahead of your trip, and ask for special meals,
many of the sit-down (i.e. not fastfood) restaurants at the park
will make special foods.  I'd call or write and at least ask about
bringing food in.  If anyone ever tried to STOP me from taking
Alyssa's food somewhere, they'd get an earful!  And, I'm not a
pushy or loud personality, normally!!!

Tijuana, I'd worry about - I don't have any idea what the food
labelling laws might be in Mexico, maybe you can find out... but
you'd need the Spanish words for milk ingredients, at the very least.

Have fun, and good luck with the food.  It makes everything just
a bit harder, but it's still worthwhile!

Laurie (and Alyssa, allergic to dairy, eggs, peanuts and walnuts)