Playa Tamarindo-
The nicest boutique hotel on the entire coast in Capitan Suizo, south end of beach.
Manual Antonio-
I like the lodge feel, Costa Verde, two great pools, and lovely gardens and views, some are separate cabinas with private terraces and patios.
10

ticotim
11

spin
On Christmas Day, the Ticos flood out of the San Jose area and head for the beaches. You will need to make reservations!!! I like Tim's choices. Most of the adventure activities you mentioned above can be accessed from Tamarindo by heading to Rincon de la Vieja for a day to two. Enjoy
12

costaricablog
I wouldn't call Tamarindo 'great'.
If you fly into Liberia Airport then its a 30 mins drive to the beach at Hermosa or Ocotal.
Your mum can do the mud baths at Rincon de la Vieja
Pro tip