It is the cut of the diamond that determines the brilliance of the stone. Above all you should select jewelry she loves to wear. The problems that jewellers have in resizing rings with soft stones such as coral, pearl, opal and many others is that they will be instantly destroyed by heat from a jeweller's torch.
Explanation of Cut, Color and Clarity of This Diamond
Cut Quality Diamonds cut to ideal proportions are made to reflect the most amount of light. This results in a display of brilliance and fire, thereby placing ideal-cut diamonds higher on the quality pyramid than deep or shallow-cut diamonds. Ideal cut diamonds have most intense brilliance of all diamond cuts.
Color Color grade I is in the middle of the near colorless category. Typically a trained professional will be able to discern the presence of color. Some people prefer warmer colors like I. When I color diamond is set in yellow gold jewelry used with yellow gold bezel, the diamond will appear as gorgeous as any of the higher graded stones.
Clarity Inclusions and external blemishes in diamonds of SI1 clarity may be easy to spot under 10X power magnification. Location of the inclusions greatly affect their visibility to the naked eye. SI1 diamonds of good color produce as good of a sparkle as the more expansive VS graded stones of lower color. Excellent bargains may be fond in this category.