I have bought a couple of kits, and lots of yardage from Jinny Beyer. I haven't had any problems with the fabric bleeding, etc., but there is always a first time. I don't usually prewash anything because I like the hand on unwashed fabric. I would hate to have to starch and iron a new piece of fabric.
I like the instructions that comes with the kits. They are clear and concise. And she does post any 'mistakes' to the pattern online. I would think you might contact her customer service people and ask them about bleeding etc. I bet they would help.