Bring your own gluten free ice cream cones for the soft serve ice cream. They don't always have cups and they don't have gluten free ice cream cones on board. Just carry them in a plastic tupperware. Easy to put the tupperware in a bag and carry it with you in case your daughter is in the mood for ice cream.
As mentioned beforehand, the buffet has GF food. They also had a sign for deserts that have GF versions that they can get for you. For quick serve on Deck 9 - for pizza, just remember that it will take about 15-20 minutes (so order ahead of when you really need it) as they have to make one from scratch from the GF dough.
For dinner, they will bend over backwards to try to accommodate you. You can ask for GF bread and a separate sauce for the bread (so people don't cross contaminate with their normal bread). In addition, the chef can make some special deserts for your daugther. Alternatively, if there are any GF deserts that are being served in other dining rooms (not just your assigned dining room), they can also go get that for you. In addition, if there is a desert that has some gluten items on it, they can specially make one for you without the gluten item.
If you are going to
Castaway Cay - they will ask you to preorder the food the night beforehand and tell you to pick it up at Cookie's One. This was the one area that's gotten some controversy. Before, they used to make it on the ship and deliver it to Cookie's one. Now, they've expanded the kitchen at Castaway and will make it at Cookie's One. However, on our visit earlier this week, they did not make it at 11:30 when the restaurant opened. They only started making it when my wife arrived. This resulted in a long wait (where I had time to take pics of the ship while my wife went to talk to the person about her food, stand in a long line, and eat half of my food - all before she got her food). This defeats the purpose of preordering the food. I'm not sure if this was standard operating procedure or just a hiccup. Needless to say, I've voiced my concern.
For your second question - my wife refuses to try other cruise lines because of her gluten allergy and how well
DCL has taken care of her so far.