---The Backstory---
At a young age, at some point in her abusive childhood, she was exposed to high levels of radiation. She's not half super-mutant, but rather just mutant. (Mutant as perhaps what sort of appears in the xmen world.) It's my opinion that Cait's vanilla story is bit generic. A drug abusing irish gal that fights for a living is a character that can be placed in a lot of games. But suffering from the long aftereffects of radiation is a characteristic that I think ties Cait's story uniquely into Fallout 4. Also I find it to be a bit of an ironic addition that a character from Ireland is now green.
---What This Mod Does---
Her skin now has a green tint to it, and close proximity to her will result in a slight intake of radiation damage. This radiation is felt not just by the player, but other NPCs (but not settlers) -- such that her venturing into establishments such as diamond city and good neighbor results in shootouts between her and the residents. I find this to be a great addition to her character, because what more can push a person to "be a junkie" than causing radiation damage to those around?
Now, to add balance to a companion that gives off radiation poisoning, Cait now holds the Iron Fist perk of rank 3, the Big League perk of rank three, the Basher perk of rank 2, the Strong Back perk of rank 2, and a Strengh Level of 10 (the vanilla level is 5).
The only dependency is Azar Ponytails. (For the dreads, of course. Its a must have.) Furthermore, I've opened up Cait's vanilla corset in Photoshop and made a few tweeks, such that her clothes better fit the green skin hue. To find the corset (if lost) search for it with help "corset" 0. My CBBE preset for her is also included in the download.