Sadly the Periphery- and by that I mean the smaller groups out there, not the larger nations like the Marians and Taurians- didn't get a great deal of ink. There's sections in the Periphery sourcebooks, Field Manual: Periphery, and Field Manual: Updates, and some get small mentions here and there in other books. The Field Manuals are probably the best bet in that regard.
I seem to recall Susie as being the antagonist in the Mechwarrior 3 expansion Pirate's Moon, but it's been so long since I played that one that I'm not totally sure anymore.