How to tame that wild mane?

I have a pony whose mane went ungroomed for many years. Now she's going into the dressage ring and I need to shorten and thin it for braiding. Only problem is, it is thick. THICK-thick. I've been slowly thinning and shortening it over the past few weeks and finally followed the advice of a friend and shaved a good half inch of width off of it on the bottom side. It has helped a lot, but along with that I pulled it to the appropriate length. It looks pretty good, but sadly it's STILL too thick to braid. They are enormous and bulky and messy-looking. How can I improve this?