Hi Paul,
Using flash in daylight conditions can create some wonderful results, but there are some challenges that go with the territory too. One of the biggest in using flash outdoors on a sunny day is that most flash units don’t have that much power by comparison to the sun (who would have thought!). Compounding this is that fact that as you move a flash further back from the subject, a small factor called the “inverse square law” means that every time you double the distance between the flash and the subject, you actually get one quarter of the amount of light energy reaching the subject.
Compounding this all is the cameras maximum sync speed of 1/250th of a second; this is the fastest shutter speed at which the shutter fully opens when the flash fires. At shutter speeds higher than this, the rear curtain starts closing before the first curtain has fully opened, and the burst of flash energy will only illuminate part of the image sensor.
Some cameras and flash systems do permit flash sync at higher shutter speeds, and this does allow you to use wider apertures, but there's a catch; to do this, the flash has to pulse its energy several times throughout the course of the exposure, and rather than making each pulse full-power, it can only use a fraction of the power output.
It is not a perfect solution. With a camera set to work at that daylight exposure of ISO 100, 1/250th of a second at f/11, a Nikon SB700 flash working at full power will have a flash range of three metres. If you adjust the camera’s flash settings to work at the High Speed Sync, and then adjust the exposure to ISO 100, 1/2000th of a second at f/4, the actual flash range drops to 1.3 metres at full power. You can work with the aperture moderately wide open, but you'll need to have the flash close to your model, and the close proximity of the light will cause uneven lighting.
To achieve the best results in bright daylight, professional photographers actually use a LOT of flash power (usually professional light systems that pump out well of 20 times the energy of your flash). They then pump this light through large diffusers or “soft boxes” to remove the hard edge off the light, and to help matters even more, they also have makeup artists on hand to remove bright highlights on the model’s skin.
My advice as you head out to make more portraits like this, is to work later in the afternoon, or early morning. Position the sunlight behind your subject, and then us the flash to fill in from the front. I have a hunch you did soften the flash light in this instance, and I would continue to do this.
As for other technicals with this image; given the chance I would just make sure there are no trees growing out of your daughter’s head the next time you go to photograph her, and I'd also use an adjustment brush in Lightroom to tone back the bright skin on your Charlotte’s arm. Otherwise, this is a good effort.
Cheers, Anthony..