From a lighting perspective, there's not a great deal to say other than you're getting the hang of this flash malarkey pretty quickly
More of a pictorial kind of crit than technical (maybe re-post in portraits section?) but I like that shot a lot. Good composition, nice DoF, pretty girl - so just comments really. The flash is perhaps a tad strong and as a rough guide, flash outdoors tends to look better, and less obvious, when a bit under-exposed. You can get away with it here as the flash looks pretty much like bright sun coming through the arches. Shadows are quite hard too, matching the sunlight. Personally, I'd fix the brightness by pulling down the highlights slider in Lightroom, perhaps just locally around face and hat.
The other thing is the eyes, and regardless of whatever other visual distractions there might be, the eyes are always most important in portraits. And she has lovely eyes, but hidden behind the reflections in those glasses. Getting rid of them in-camera would be very difficult - you'd need a
huge black reflector. You could spend a few hours in Photoshop fiddling with the reflections and toning them down, but it would likely look a mess. In that situation, I think I'd ask her to take the glasses off and hold them as a prop, to go with the sun-hat. If this was a semi-serious shoot, maybe you have other examples without glasses, different hats etc?
Were you in high-speed sync mode? Shutter speed must have been close to it.