She is definitely red based, I'd do a white pattern panel (ie one that tests for every white pattern) plus cream, dun, and agouti. Agouti doesn't have any visual effect on a red base but it's interesting to know if you ever plan to breed her (as it determines whether she can produce black or bay when bred to a horse with dominant extension). As for cream vs dun, I'm not convinced she's cream because of how dark her mane is in the coloured part, but I'm not convinced she's dun because her ears lack darker bars on the back. As for other dun factors, she's white where all of them express, so she won't show them regardless.
Her white pattern/s MIGHT be colour shifting her to a lighter shade of red, so she may not be cream OR dun, but if she is, you'll know if you test for them!
She is not champagne because her skin is black where she doesn't have any white. Champagnes have speckled/salmon coloured skin.
MAKORA THOROUGHBRED SPORTHORSES