I have reactive hypoglycemia...which means that if I eat too many carbs (which are sugars and starches), my sugar shoots up. Body overshoots the insulin, and the result is the hypoglycemic crash. The solution to this is to avoid concentrated carbs and be sure to focus on proteins which are digested more slowly and maintain a much better blood glucose level longer.
I actually have no problem on the ship as there is plenty of good quality protein available. I probably eat better on the ship than I do at home.
In my situation, avoidance of a problem is FAR better than trying to treat it. If I do a sugar boost--as in orange juice, candy, etc. I know that my sugar will instantly go up, but then I've set myself up for another crash. Thus, I want to do some protein food at 3-4 hour intervals. Treating earlier with protein is better than treating late with glucose.
SO...on the ship....breakfast--not cereal and milk! I can get cottage cheese with various toppings at the buffet or I can get a good sit down breakfast. I will sometimes bring a bowl of cottage cheese back to the refrigerator in the room.
Lunch...again, I prefer the sit downs. Will try to time this about 4 hours after breakfast. If you like the buffets, there is plenty of good protein there too.
Late afternoon snack..we have late dinner by choice, so about 4-5 pm, I'll go to Goofy's Galley and get a chicken wrap or turkey panini or whatever.
Dinner--8:30, meaning food about 9 or a little before.
Room service is available 24/7 except during the safety drill and on the last night, but 30 minutes is too long to wait if your wife is in an acute situation. Sounds like your "peanut butter to go" would work well. You can also get a "all hands on deck" platter from room service and wrap up the cheese in saran wrap...it will keep for a couple days in the refrigerator.
For excursions or whatever, I keep a Zone Perfect bar in my pocket or purse. They are about 13-15 grams of protein per 200 calories, and don't taste like cardboard. 1/2 of a bar is a good snack and keeps me from crashing.
The only time I have an issue on the ship is when I bring it on myself...like when I just "have to" indulge at the dessert buffet. Keep the protein handy for that.
I don't know if any of this will correspond with your wife's situation or be of use to her, but...that's what it is.