Call in and add it to your reservation ASAP, and every time you call in for anything make sure they can repeat your allergy back to you.  Ask to speak to the special needs department to get more allergy information.  Choose a set dining time each day, not the freestyle option, so you have the same servers each meal. (If those servers aren't good with allergies, request new ones ASAP.)

Always check everything brought to your table.  Every single thing, every time.  You should be able to pre-order meals for the following day.  If not, request to do so.  Bring snacks for port days (and possibly for on the ship, too.) 

Best of luck and have fun.

Four-day Cruise already booked as a "family surprise". MIL says she asked if they handle food allergies. At this point, we are only avoiding PN/TN.