Costa. Fly into Liberia, and bypass Tamarindo, place is a dump. I would stay a few nights at Hotel Playa Negra. Great restaurant, cool little bungalows to stay in, and 2-3 other quality places to eat in "town". World class surf right out front. Can do canopy tours, ziplining, waterfall tours, horseback riding, etc... Go up to Avellenas for the day, she can sit at Lola's or explore the rivermount area while you surf (its a 10 minute drive from negra).
Then go down to Nosara for a few days. Never been, but apparantly there is more of a town/social scene there, and it isn't as dirty as Tamarindo. Waves still fun there too. good luck, i take my fiance there every year and she loves it.