HI Annie,
Here area few suggestions:
You might enjoy spending an afternoon at Loterie Farm on the French side. Its on Rue de Pic Paradis, which intersects the main road between Marigot and Grand Case. It has a private pool, rain forest nature hikes, zip lines and dining. Check it out at
www.loteriefarm.com. Pic Paradis, which the highest point on the island, has great views and is a nice hike but there used to be security issues there. It's been a while since we did that hike, and I have no idea what the situation is now - someone else can probably chime in. If it can be done safely, it is a unique and fun experience.
Cupecoy beach (on the Dutch side past Maho near the border) is a series of small, unique beaches surrounded by beautiful low cliffs. There's a beach bar at the entrance run by a local named Dany who takes good care of everyone. Just FYI - you may encounter some nudity at Cupecoy, but people there tend to be very chill.
Harmony Nights should be going on in Grand Case while you are there (it runs January through April). It is a street festival that happens every Tuesday evening and has lots of food, vendors, and entertainers. Parking can be a bit of an adventure, but there are lots of people and lots of security around. We usually park on Route de l'Esperance, which is the road to the Grand Case airport on the north side of town, and walk into town.
Have fun!