The only way to really get an answer is to get her tested. There's only one lab that tests for brown (PetDNA), and you can test for various pinto markings at UC Davis. Individually the tests aren't super expensive, but they can add up quickly if you're doing a lot of them!
As for my opinion, I think she's probably bay. I don't see any lightening by the elbow or stifle, which should be evident in the winter coat. However, if she changes significantly in the summer time, that could indicate that she's brown. With the bottom-heavy face markings, she could have splash, but pinto markings are not my forte