Freezing made up sandwiches for days at a time is not a good idea . they will become soggy wilted and off flavor .. why not plan on making up an attractive platter of cold sliced deli meats and cheeses like turkey ham , salami swiss cheese american, cheddar along with rolls/,marble rye , pickle, olives ,mustard mayo they can make up their own sandwiches fresh ,also make a couple of dips and have some fresh veggies like baby carrots ,broccoli buds celery sticks, cauliflower buds & chips ..you can buy a bag of cheese cubes and stick each one with a pretzel stick put on a pretty platter for finger foods egg salad sandwiches with bacon and homemade chicken salad is very inexpensive to make and delicious but does take some preparation ahead of time large sheet cakes are also simple and easy can be baked frosted and served in the same pan can buy throw away aluminum pans at the dollar store the cake CAN be made a couple of days ahead of time also salads like potato salad,. baked beans coleslaw ,3 bean salad,macaroni salad( Do not make anything with tuna ahead of time it deteriorates quickly ) can be made two days before the cake and salads are where you can help out and prepare for the buffet .. Your niece can make most all these up the day before herself there really is not alot of cooking just preparing ahead of time and getting organized, getting things ready ,.she can make a list and check things off..with you offering a helping hand I am sure the christening will be a success . and everyone will love the food . and not get food poisoning LOL.