What ISO were you shooting at?
By the looks of things you were shooting around Noon (can see the shadow on the eve of the house) and your flash did fire (can see the hard shadow behind her).
An ND filter would have helped with the ambient lighting. (adjusting the shutter is how most folks do it and long as you do not to to MAX shutter speed) even if you do and you start to get a little banding try an old trick, flip the camera upside down and take the shot , if the banding in on the bottom of the shot it may not show up too much.
You could have moved her to full shadow area and then lit her up with a reflector or the flash.
Last thing is to get a little more powerful flash/strobe to overcome the ambient. (that is why they are expensive)
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Shoot well, Joe