The truth of the matter is, you're not going to get an cleaner, or more natural than water. (Unless of course, it's bad water. 0.0)
I think think cleaning it out with water, then some conditioner, will do it good.
You say you try not to brush her mane- A little tip, if you ever have to brush her mane or tail- do it when it's wet. The hair gets stretchy when it's wet, so there's much less risk of splitting and breaking the hair. It'll just stretch. :)