From my understanding, a horse is un-register-able unless one or both parents are registered. With not knowing either parent or even her breed, there is no registering her.
Although some 'color' registries like PHBA (Palomino Horse Breed Association), I believe, there is a possibility of registering with a bunch of 'IF's' but I could be wrong though.
But with not knowing anything about her past and if she has no tattoos, brands or any other man-made mark, it's next to none getting her registered. Sorry to be of not so good news.
Papers don't change the value of your horse to you and she is probably a great horse
We do like pictures here too by the way
Edit: I must type slow, LOL. Forgot about PtHA!! That is a perfect possibility! She sure is pretty