Windstar is awesome on this issue! Just cruised for 14 days and we are gluten intolerant. You tell them when you book and reference that on the special needs form they send you and, when you are onboard, they do the rest beautifully. The first meal you may need to remind them, but they say they can do anything GF. We were given the next evening's menu to select from and leave with the chef and then our choices were confirmed briefly when we arrived for that dinner. It was great to have delicious sauces and gravies again with no worry! Also, the staff is there to question about what you can have other times of the day, although the buffet lunch items should be carefully perused as we found an occasional confusing label, quickly corrected.
Their GF bread is okay, but nothing special, but they have it easily available - just ask. The "plant-based" offerings which have no gluten, salt, sugar, or oil are a choice at every meal. You may cruise GF with Windstar with no hassles!