I use Show Sheen as well, it is a great detangler and it leaves an instant shine.
You can also work some Mane N' Tail conditioner into the hair. It makes it alot easier to comb/brush out, and it keeps the hair from sticking together as much. You should be able to find this brand in just about any feed/tack store that sells horse shampoos and conditioners.
Try washing her mane and tail and shampooing and conditioning it. Wash the shampoo out, but not the conditioner. You can also try to braid the mane and tail after you wash/comb it. You could put a tail bag and slinky on her to keep the braids neat and flat, but if she is turned out they might get lost or ripped.
If you are just trying to manage her mane and want it to be less tangled, but don't need a perfect mane all the time, then just braid the hair and forget the bag/slinky.