The thing about being goth is that it's not about wearing black. That's just on the surface, but goth identity is about more than aesthetics. Do you go home and contemplate the macabre? Who here identifies as goth? Do you watch Dracula and Nosferatu in your free time? Are you listening to Mozart's Requiem in D minor as your "happy music"?
Goth couples are even more special than just being goth as an individual. It's not everyday you find someone interested in the dark and disturbing as you are. To form a bond and connection over the medieval, the macabre, and the morbid is something most people don't want in a partner, and that's what makes couples like goths so special. So instead of buying her a fresh bouquet of daisies, or a basket of roses, consider dried flowers that have lost all their color and luster. Consider buying her a black or white lace dress instead of something more colorful. Regardless of what you choose, it's important to appreciate the goth girl or boy you have in your life.