I'm getting married myself and going through exactly what your friend is going through. One thing I found was that diamonds are cheap in Nepal. It may be due to the fact that diamond price greatly varies based on its cut, color, clarity and carat (they call it 4 c's of diamond).

http://www.diamondideals.com/education/find/four_cs.cfm

In Nepal people usually do not ask for these factors while buying diamonds, while in US, these factors play huge role in their price. High clarity diamonds are ridiculously expensive here in US.

After doing some research, comparing prices among kay vs bluenile vs "local jewelry district in boston" vs "new jersey indian jewelry store" vs "nepal ko store", I have made up my mind to buy it in Nepal itself. Its cheap and nobody cares about 4c's. Anyways diamonds are overrated and carry low resale value.

Just my two cents.