What color are the horses eyes? What color is it under her tail? If her eyes are an amber color now and they started out being green it is a very good chance she is a champaine. I have a classic champaine. When she was born her eyes were a bright blue color and then by two months they turn the prettiest green but by the time she was a year they were amber. She has a darker mottling around her muzzle. It looks kinda like freckels.
When I had her regestered as a Champaine, I had to take pictures of her eyes , under her tail as well as her body. Under her tail is very pink. Her mane is flexen because she also has the silver dapple dilution gene. Her body is a taupe color with dark points. She reminds me of a buckskin in her coloring. I know everywhere I ride her people comment on her color too because it is so unusual.
Golden Champagnes tend to have the very golden yellow bodies, although they vary from a darker golden or even redder (confused with a sorrel) to pale and lighter. Manes on a golden champagnes someetimes red or gold instead of white and horses with these darker manes and tails are likely to be registered as a sorrel instead of palomino or goldchampagnes because people didn't know to much about champagnes or that color.
If you want to find out more about Champagnes Phil Sponnenberg, DVM, PhD has article on Champagnes. It is called Champagne Dilutes: Definition and Classification.
Another great article to read about Champaines in general is, A Horse of a Different Color, I have enjoyed these articles having a champaine mare myself.
I hope that this will be of some help to decide what color your filly is.