I voted a resounding YES!
I did not fly to Europe with my when they were that young (only because the oppurtunity was not there) but we DID fly to Hawaii for a wedding (which is longer from Michigan than east coast is to Europe). It was really not hard. Long haul flights have always been easier for me with the kids because the food and entertainment are so much better. Neary every airline to Europe will let you request a kids' meal (seems DS always gets chicken nuggets) and most European lines also hand out little toys and games to the kids (plus movies of course).
If you are going to any bigger cities in Spain (and this applies for Paris--haven't made it to London yet) if your DD really will not try new things (I understand, I ahve a picky kid--but he loves jsut about any bread product so we just always hit local bakeries

) it is (sadly) very easy to find McDonald's, Burger King, KFC and Pizza Hut. In fact, standing on the steps of Sagrada Familia in Barcelona my kids felt compelled to sing "A Pizza Hut, A pizza Hut, Kentucky Fried Chicken. . ." becuase you could. in fact, see all 3 chains in the songs from that spot

Also if your DD will eat pizza, taht is widely available even in small towns in Spain. Better yet, fresh bread and fresh fruit, yogurt, cheese, etc. is always easy to come by (just shop for Sunday on Saturday--no grocery stores open on Sunday!) and pretty healthy,
We often travel at Christmas. Even when the kids were very much believers, it was not a big deal. We took stockings with us and Santa would fill those and leave bigger items at home for us.