You can really divide the manufacturers in 3 camps...
Those who design the WSD ground up, i.e. different geometry, but more important different carbon fiber layup. For many women, the layup in a unisex frame is simply too stiff and over reinforced, a woman in general will weigh less than a man of the same height and will in general put out slightly less power.
Then you have manufacturers, that take a unisex frame, change the components to make it a bit more suitable
(saddle, handle bars width, etc.
)
And finally, you have those that sell a unisex frame with same components as the mens bikes, but just slap some pink accents on it.
With all that said, don't just assume that you need a WSD just because you're a woman... it's not that simple. You could argue that the shorter you are, the more likely you are to benefit from a WSD, and the taller you are the less likely it is that it will actually be the right choice for you.
Also, are you sure you want a dedicated tri bike? For most, it makes much more sense to get a road bike... keep in mind that a tri bike is very specific in what it's designed to do... it's kind of like a sports car, very good at one thing only, but a horrible transportation for a family, no storage, etc. whereas a road bike can be very fast, versatile etc. kind of like buying a high performance sedan, able to move the family and all the bags needed for a long weekend.
If you plan to ride in group rides, organized rides
(centuries, charity rides, etc.
), then you need a road bike. If you plan to ride by yourself
(or with a tri group only
) and only race tri's, then a tri bike might be the best choice.