he's removing the background anyway, so I doubt color temperatures matter.
To the OP, do you have an off camera trigger for your flash? if not, I'd consider it or at least a cord so that you can have your flash a little farther away from your camera. That will help with the flatness of the lighting. If you're at all worried about color temp, a gel on the flash will solve that.
Personally, I would reshoot. Your model is "in-house" so it shouldn't be a problem... I'd give her a slightly different pose and demeanor, considering she's holding a handgun... she looks too cute with that pose. Have the two umbrellas on the background and either shoot portrait with the camera turned to the right so that the light matches the shadow slightly better, or if you can, get the flash off of the camera.
my 2 cents