Sorry, I think we are not communicating. I know she is not 'in the game', however, she is in Pregen, and images, thus I might be able to add her in my game using a MOD similar to the Custom Character Mod.
I actually got in contact with Zeltop and was able to add Lilith using the Custom Character Mod that he wrote a guide for. This is just as a Custom Character, not as a Vanilla Story Character.