Take care of your diamond by avoiding breaks and scratches and keep it clean. As for size, make sure that she would be comfortable in a larger sized ring and then purchase accordingly. In some traditions, nothing the woman wears should outshine her ring.
Explanation of Cut, Color and Clarity of This Diamond
Cut Quality The ideal cut diamond is a very precise mathematical equation, where diamond proportions and angles are cut to optimize the diamond's superlative optical properties, in particular it's high refractive index and color dispersion, to create a diamond of unequaled beauty with perfect balance of brilliance and fire. In layman's terms, the diamond is cut to make it the most beautiful diamond so it retains its intrinsic value.
Color Trained people can see yellow in a J color diamond pretty easily. You can also do this by placing the diamonds upside down on a white piece of paper and looking at them from the side. J-color diamonds offer an excellent trade off for price and quality - excellent choice for the budget conscious.
Clarity Diamonds of SI3 clarity are on a borderline between slightly included and included diamonds. SI3 grade inclusions are almost obvious under 10x magnification. Inclusions in such diamonds may be noticeable to the unaided eye. However, when observing the diamond "face up" as it is mounted in a ring, the inclusions are usually not visible.