Please don't be devastated - celiac's is an awful thing to have but once you and your daughter become used to the condition it becomes a part of life.
I went to WDW for the very first time in April 2009 and was diagnosed with celiac's 3 weeks before my trip after years of stomach problems. I was horrified when they told me the amount of foods I would have to avoid from now on for the rest of my life, particularly as I was going to WDW a few weeks later! I had made all of my ADR's and was worried about counter service more than anything.
I needn't have worried, the staff and the chefs at Disney were fantastic! I rang up Disney Dining and explained that I had now been diagnosed with celiacs and they noted this on all my ADR's. I made sure I reminded the CM when checking in, and in all the TS restaurants the chef always came out and told me what was and wasn't gluten free on the menu, and in many cases they were willing to make many of the menu items gluten free for me.
And as for counter service, I just queued up and asked the CM's what I could have from their menu that was gluten free - many of them provide gluten free buns and things for hamburgers and hotdogs, which may be good for your daughter if she enjoys those foods. If she will eat a better rang of foods, I found Cosmic Rays particularly good, they have a chicken, vegetable and mashed potato dish which is sooooooo filling!!
As one of the other posters mentioned, try the Disabilites board on here as I found this board very helpful before going to WDW.