It's going to depend on two things...
The first is: Did she inherit a recessive buff gene or a recessive brown gene from her parents? You could do genetic testing to figure that out, or you could just cross your fingers and see what happens when you breed her.
The second is: the coat color (and any recessive coat color gene) of whoever you breed her with.
and also be sure to read http://www.zimfamilycockers.com/breeding.html
before going down the road to breeding her.