I dont have an 8 year old however, even despite that i dont think i could cope withmy child so far away. If you're feeling emotional already and she hasnt left yet that might be your clue
Your dad sounds so generous what a lovely man! Is he paying? FWIW Disneyland (and the USA, despite all the sh*t thats happened there of late) is a wonderful place. Ive been there twice and we are consdiering spending next xmas in NY. Id seriously consider going if i were you, despite the fear of flying. If you can id consider some hypnotherapy to help you conquer the fear. If someone offered me a place to go, id be gone in a second!