Upload & Sell: Off
No pop-up flash will produce anything close to desirable results.
Beyond that, it's really a matter of deciding between:
Being "stealthy", which means shooting at ISO 6400 & using at least an f/1.8 lens or maybe even renting a 70-200mm f/2.8 lens,
Getting better images with a flash like a SB-910 or at least SB-700 but totally losing the unobtrusiveness factor.
Alternatively, your friend could hire someone who does this for a living and will give great results for... well, depending on their experience level & what part of the country they're in, anywhere from $200-$500.
That seems to me a very reasonable figure to spend to capture what will be one of the most treasured moments in your friend's life.