It will be up to her if she will let me post a picture of her. I don't know if she wants you all to see my ugly mug next to her.
Anyways, what I meant by "largest modding community," was that with, say, the Source Engine, you will have one completely converted mod come out, then here will come another. The second one really isn't that different, it's just a copy with a few changes here or there. GunGame for example is just slightly changed from the original gameplay. Rather than buy your guns, you "level up" to new guns. There are hundreds of variations of GunGame, the only difference between them is the order of the guns you get.
There are a few actual mods that stand out, yet many of them aren't that great. Zombie Mod, they change the top half of bodies to look like some sort of monster-blob from a horror movie. They also just change the gameplay dynamics, the darkness of a level, which can be changed through a mod you can get from Steam.
The most common modding I've seen on Source was the creation of maps, I've created a few myself in my high school Visual Technology class, creating a map isn't hard to do, and if you look at most maps that are created, they are nothing to gloat to anyone over, they are quickly made without much of a thought process.