They gallery doesn't show empty folders. In fact, it doesn't show nested folders either. When it does a media scan, it basically looks for any folders that contain one or more pictures, and that list is what appears in the gallery. (So, say you have a root-level folder called "MyPictures" which contains some image files. In addition, it contains a another folder called "Vacation", which in turn also contains some image files. When you go to the gallery, you'll see both "MyPictures" and "Vacation" at the top level, and if you open "MyPictures", you will see all of the images in that folder, but you will not see any reference to "Vacation" inside of it, despite the nested folder structure.
In any case, the quick answer is to put at least one picture in your "wedding" folder from the computer. Then the next time the media scanner runs, it should show that folder in the gallery.
The other potential solution is to use a file explorer app (Solid Explorer is my favorite, but there are plenty to choose from), to manually move your image files where you want them.
Note: The above behaviors are assuming you are using Android 5.0.x's built in "Photos" app, since you're using a 2013 Nexus 7. For anyone using another device that might have a custom image viewer instead of the stock one, or anyone using a 3rd party image viewer, mileage may vary.
