This is a decent shot. I don't think the flash is that bad. She looks to be at about the same brightness as the background. I would probably have brought down the exposure on the background just a little to make her stand out a bit more.
Yes the light is flat (no shadows on the face to create depth) but it is still a decent picture. You have a good exposure on her face and a good skin tone.
The flash doesn't bother me as much as the sunlight/shadow line accross the sweater. You may be able to take that into photoshop and use an adjustment layer to even out the tones on the sweater. The hard shadow line is the only thing that distracts me on the image.
She is a pretty girl and you did get a nice shot of her. If you were to take the flash off camera and have someone hold it or put it on a stand or clamp it to something you could get a better angle and create some shadows on the face that would add depth and modelling. It would give the portrait more depth and more of a 3d look to it.