To my knowledge, dreadlocks were not allowed by the old regs.
Mostly, the new regs define hairstyles more narrowly and specifically than the old regs. Before, the female regs stated that hair must be above the bottom of the collar, or be put up—there may have been more to it, but I don’t recall since I haven’t read it in a while. The new regs state what is acceptable in a hair style—no changes in length more than 1” (so none of the really short in the back, long in the front), parts must be straight, short hair cannot be shorter than a certain minimum, long hair cannot be put up in a lopsided fashion, etc. The new regs also state that females can only wear clear nail polish, where before, we could wear “conservative” colored polish.
I’m not sure why anyone would want to wear dreadlocks in the first place. It’s hard enough to keep hair clean, why would anyone want to make it even more dirt and germ catching?
The whole point of dreads is that they are never supposed to be washed. It's an Aboriginal/Rastafarian thing.