Brian,
Which aspect of this do are you finding difficult?
The exposure looks fine to me. I opened it in photoshop and saw no clipping. You could bring the whites down a tad, but basically, I think it's fine.
If you are referring to the difficulty in bringing out detail in white flowers: assuming good metering, which you have, this is usually a matter of the angle of the light and postprocessing. I agree with John--using a reflector could help, as you could direct some light from one side, which would bring out textures and lines. You can also do this with diffused flash. I do most of my flowers indoors, and partly for this reason, I almost always have at least one light coming from the side. I'll post below an example that shows how light that is not straight on can bring out details in white flowers. I took it outdoors, in our garden.
You can bring out the textures more in postprocessing, if you don't overdo it. In Lightroom (you don't use this, but a lot of folks on the forum do), you can do this with the clarity slider. With other software, you can make a local contrast adjustment. See
this post for an explanation of how to do this with unsharp mask sharpening.
I disagree with Steaphany. Flowers are one of the main things I do, and I don't even own an incident meter. You can meter this well with the reflective meter in your camera, but if you goof, you will see it, and you can just re-shoot with a changed exposure.
Dan