Umm I'm not sure the top of the line flagship is really needed for someone who just takes photos.
Assuming you're referring to the S6 Edge + or the Note 5, you've identified the difference. If she doesn't use the S-pen, the the Note 5's extra features are a bit wasted. However it is cheaper and more comfortable to hold. If she thinks the Edge screen is cool, then I suppose that's a reason to get it. Otherwise between the two phones, it seems like she should get whatever is cheaper.
However - if all she cares about is the camera and nothing else (as long as it's fine), the G4 or regular S6 camera is just as good and will be much cheaper. The iPhone 6S will also likely have a class leading camera, though will be at the price point of the Note 5.