Based on reading about her method and watching her do it, a couple of thoughts:
There can be a lot of threadplay (retracing your steps, etc.) doing this, so the lighter weight thread the better (60 weight is recommended.) To minimize the look of thread buildup, match the thread to the background as closely as possible. The goal of the method is to give texture and movement to the background, rather than showing the quilting. Lighter weight thread helps achieve that.
Bottom Line thread by Superior Threads is a good choice for this type of technique; I use microtex needles with it.