You seemed to match the sun quite well with a flash.
This just isnt true. She is properly exposed, the sunset isnt. They
are not matched at all. The sunset is overexposed.
This is the way I would've shot it.
Now this might not have been what you were going for, and that's
fine, we all have our artistic visions. To get your image to mine,
IN CAMERA, here is the process.
You dont have any EXIF info in your image, that will make it
difficult to give exact numbers. Let's say you shot f5.6 @ 1/100.
This was too open to proerly expose for the sunset (or too long of
a shutter speed). You would want to close down the app to say f8 or
so. That would darken your sunset to what you were probably seeing.
I would then use off camera flash. I HATE on camera flash fill, but
if it's all you have it will work. I would either bounce the flash
off a gold reflector or use a gel. Gold reflectors should work
depending on how much light you are getting. Silver might work just
as well reflecting the gold tones the sunset is giving off already.
The reason for all this gold is becuase flashes are daylight
balanced, not sundset balanced. A sunset gives off gold/orangish
light and "daylight" is a whiter light. If the subject is lit with
white light and there is gold light behind her, it will look
unnatural.
Hope I've helped. Oh yeah, here's a side by side.
GageFX
Shooting directly towards the sun is one of the toughest things to
to. You probably aren't getting alot of response due to the fact
that you picture is pretty good. You seemed to match the sun quite
well with a flash. You might consider using a gold reflector in
that type of situation. One soft white reflector on one side one
gold on the other sun is you edge light no on camera flash. Thats
one way but it would require more gear but at least no electricity
in the water ;-) Plus it always makes sense to use the sun instead
of fighting it.