Judging from the pictures and what you said, I would say she was amber champagne, which is easily and often confused for buckskin. I know nothing of POA allowed colours or anything, so I'm not sure that's allowed, but that's what she looks like.
Well this "old woman" learned something new!! I did a search on the internet and found that the AQHA has included the Champagne color for registery. And Amber Champagne is one of those accepted colors.
Sorry for your loss. That must have terrible, though I must say I think she was very beautiul. We are lucky in australia we don't have any cougars or anything like that but occasionally a horse is killed by snakebite, or maybe a dingo pack might kill a brumby, but she was very beautiful. I hadn't heard of champange, you learn something new everyday