My fiancee accidentally banged her hand against a wall, hard enough where one of her 4 prongs bent. Should we be worried that the diamond may be damaged/ scratched as well?
Yes, it is possible. Diamonds are hard, but not indestructible. More easily done with direct blows like banging it hard against a wall. If you have a loupe take a look, or go back to your jeweler and have them inspect it for you. Is it insured?
Homer is right. You can scratch and/or chip/break a diamond.
Get that ring to a professional for a complete inspection and prong staightening ASAP! A bent prong is a disaster waiting to happen. Especially in 4 prong solitaire settings. You could be looking "for" a lost diamond, and not "at" a scratched one.