You had me at GF! My wife has Celiac and we've cruised Carnival 12 times but never on the Radiance out of Long Beach, rather the Panorama.
DW gets treated very well GF wise by Carnival but there have been occasional OOPSIES!!
Usually cross contamination, so she avoids buffets and salad bars.
Anyway, have a great cruise with your sis and I look forward to reading about your GF experience on the Radiance!