If you have to stay in Tamarindo, the Crocodile Hotel is right near the rivermouth and features an excellent bakery on site the first floor, ocean side rooms are really nice (or seem to be). If she wants to learn to surf, the surf camp is right there, as is the rivermouth which is a great beginners break.
For your purposes, Tamarindo will probably be flat, and if its not, Playa Grande will still be better. It is about a 15 minute walk down the beach (or a 15 minute drive). Just look for the yellow house. Langosta is about a 30 min walk in the other direction. Watch out for the Manowar (Shacky got zapped pretty good there). There's a kick azz empanada place on the way to Playa Grande, so you may want to drive at least once (ask Shacky about the empanada place!).
If its happening, you'll want to surf Playa Negra, and the Playa Negra Hotel is definitely girlfriend friendly, albeit a bit pricey. If Negra is closing out, check out Las Olas in Play Avellanes. Both are about a 20-30 minute drive to Tamarindo depending upon the roads (mud or not). I've seen Playa Negra at DOH and it is world class. During this time we went and surfed head high Avellanes and had a blast. I've stayed at Las Olas a few times and really like it alot; good people, and good food. You'll like Little Hawaii and the Rivermouth, but if its good you'll surf Playa Negra mostly. If you get skunked, its a slow moving, 45 minute drive to Marbella. Marbella saved our trip, but leave NOTHING in your car; many thieves.
Never did Witches Rock, but I know that Ventura Local had a great session there.