I can't help you with the food portion of your post, sorry.
Yes, no swim diapers are allowed in any of the pool areas......the pool areas are not chlorinated as much as they are on land and sometimes are just plain sea water. No way to protect against anything. And swim diapers are NOT leak proof. If there is an accident in a pool area (visible poop like looking at a baby ruth bar under water),the whole area is closed down for a thorough cleansing depriving everyone else on the cruise of use of that area until it is reopened which can be up to 24 hours. Not fair to those who follow the rules. As I said earlier, swim diapers are not leak proof......if there is bm in the diaper while in the water, the water will flow through the diaper and contaminate the water. Your TA needs to be better educated on this subject.......check out the CDC website for information on pools on cruise ships and swim diaper use.
You can bring a small, blow up pool (check out Wal Mart and Target and KMart) that is small enough for her to splash in and you can use it as a tub in the shower for you to bathe her. Search "duck pool" on google. You can fill the pool with water from the shower (for her bath). On deck, you can fill it with a small bucket (ask the bartender for a bucket like in a bucket of beer) and fill it with water from the shower near the pool. Then, when done, you can empty the water into the drain in the shower or a drain on deck. Do NOT empty the water into the pool area.
As for diaper changes, some of the handicap restrooms on the ship have a diaper changing table in them......if not, find an isolated area on deck and change them there.....just be sure to dispose of the dirty diaper correctly (either take a plastic bag and put it in there to dispose of it in your cabin) or dispose of it in garbage can......on one cruise a friend of mine saw someone change their baby's diaper on the lounger and just leave the diaper under the lounger.......GROSSS!!!!!!!!!!!!!!!!!!!!!!!!!!!!
If you notify the cruise line prior to the cruise they will provide a pack and play for your cabin.
Hope this helps some.