@Ghislaine @BroDrillard @poastoak @PunishedD @WashedOutGundamPilot Buy a stone she will want to wear and put it in a setting that reflects her taste.
Diamonds crack as easily as cheap quartz: go corundum (sapphire or ruby) for the best balance of durability and resistance to scratching. Alexandrite of chrysoberyl is even tougher. Diamond doesn't even crack the Top 5.