What is the best ay to level (2) 9x13 cakes?

Yes, Walmart or your local grocery store bakery should give, or sell you (for pretty cheap) a box. I would take the two cakes and flip them over so they are upside down side by side and then frost them. If you have any droops anywhere on the cake you can always fill them in with frosting.

I would suggest that you ice the two cakes as level as possible.

take the edible image and I do understand that it is edible . This is a suggestion, mount the edible image on a custom piece of cardboard that is very level. Place the cardboard with the edible image, on the top of the cake. It will be very even and level because the cardboard should be firm. Decorate around the cardboard with icing, to make it blend in, and so it doesn't show to be a separate piece.

When ready to slice the cake remove the edible image as a souvenir gift to the lady.Then you will not have to destroy the image at all when slicing.

I think this is a smart way of leveling the image and ending up with a souvenir .

A local bakery might sell you a 1/2 slab sized cake box.

Just turn the cake upside down on the platter! The bottom of it will be nice and level:) If you have 2 layers; put the tops together in the middle.......

Polyfilla, a spatula and a carpenters level should do the trick.