She's stating that, like nearly everything, we don't exist in a polar or binary realm, we exist under a bell curve.

The androgynous brain isn't simply adding another choice to the mix. It's the high point of the curve, a median or a mean.

In other words one could have 10% male or female brain characteristics off the mean, not be that statistically different from the androgynous brain yet still be accurately described as a male or female brain even though you're also wildly different from one who is 95% off that median and exhibits all the extremes of gender differential.

It's not saying that 25% of folks exhibit extremes of a gendered brain.

It's a continuum. A bell shaped curve where the "bell" is a long, slow, short hump.