FOLLY: All the hotels have Nigerian food included in their buffets so maybe one of those.
NOSA: From your email subject, what you're looking for is Nok. It is African and "exotic". Based on the content of your message, however, BLD might be it.
NOSA: 8k for both people? For an anniversary of that magnitude, you're not going to find a restaurant that's worth it at that budget if I'm being completely honest. You can take her for an ice cream or gelato date and get cocktails afterward.
If you insist on taking her out to dinner, maybe you guys can check out Casper & Gambini's. There'll be no dessert and you might have to settle for no alcohol.
FOLLY: If you go with Casper & Gambini's, there'll be no appetizer either and I'm afraid it'll be water to drink. You'd also have to let her order first because then based on the balance you'd then be able to make a budget appropriate choice.Most people don't consider pizza food but that's another option. Pizza night at Taverna is N2500 per pizza, and you can split a bottle of wine (from N5000) and with service charge, you'd still be under N10k.
Update: A reader on Twitter suggested Casa Lydia would be great for this. Just two mains and a big bottle of water to share.