Telling people to "get over it" is not helpful. According to the wise and wonderful advice in How to Talk So Kids Will Listen, and Listen So Kids Will Talk, by Faber and Mazlish (my very favorite parenting book ever), what you can do for her is listen and empathize. Give her opportunities to talk it through.
Ask leading questions or make open-ended comments, like, "Aww, it's awfully hard to do without things we love, isn't it?" Or, "If this were all up to you, how would you choose between migraines and orange juice?" And then keep quiet and listen. Throw in the occasional "hmmm" or "I see." Offer to be her secretary and write down what she says, if she's brainstorming. If she has nothing to say this time (maybe she'll just cry or pout for awhile), try again the next time she feels approachable.
Ultimately, this does need to become her choice, and at 10, she more than likely has the cognitive ability to get there. It just won't happen all at once. I have suffered from multiple food and chemical sensitivities for over 25 years now, and just hate it when my husb or daughter try to "police" my choices. Every once in awhile, in a weak moment I will eat something I shouldn't have, but I have to remind myself why I avoid that food in the first place. Symptoms are a natural consequence and a great reinforcer of better choices.
Two months is not much time to mourn a significant loss. It took me well over a year of suffering and self-education before I (mostly) adjusted to all the things I had to give up. I'd give her more choice, if she were my daughter, and sympathize but avoid lecturing or babying her when she has difficult symptoms. Right now, it sounds like she sees the choice and control as being in your hands, not her own. Terrible migraines will become mostly distant history as she gets a handle on what's really most important to her.
Wishing you both well.