No offense has been taken, but eye color is usually a good start to indicating sex. Males tend to have Orange to Red eyes and females have Yellow to Brown eyes. Eye color is not always a 100% indicator though, like you said. These traits are paired with variations in the cloaca placement and the presence (or absence) of a divot in the plastron to clearly identify sex. Also, if it is still unclear males will start fanning their parts when they reach sexual maturity, and then there is no mistaking!
I was just curious if that was really a female because sadly some people label turtles as a certain gender without regard to finding out what gender they truly are.