Oh, God, this happened to me once. I knew up front that my chances of pleasing my recip were vanishingly small. I psyched myself into it by divorcing the prompts/DNWs from my recip's identity. My advice to you is to respect their DNWs, consider using one of their prompts, but write the fic for someone else--yourself, someone else you know in the fandom, an unknown person who will stumble across your fic at some point in the future.

It's a gut punch when this sort of thing happens, but it can also be freeing. Good luck.