Here is a map of the guanacaste area that includes RED taxi fares between various points:
http://www.online-costarica.com/map/guanacaste_map.jpg. On that map, the fare quoted between the airport and Playa Coco was $20 for the 20 minute 30km trip. Playa Flamingo would be substantially more. It is listed as $40/95km from PLAYA COCO, but since part of that is backtracking from Playa Coco to the main road, I'm guessing the fare is probably more like $50 from the airport to Flamingo. This would be fine for 2-3 people much more than that and she would obviously need a larger vehicle or extra cabs.
Another slightly more expensive alternative are shuttles. Here is one link:
http://www.1costaricalink.com/eng/transportation/trans-busetta.htm. On that site shuttle rates to the Playa Coco area beaches is $25/pp (2 pax min) meaning it is much more expensive than a cab for even just one person. The rate to the Flamingo area is $30/pp, meaning if you're talking only 2 people it is only about $10 more than cab and maybe worthwhile.
Of course if she has a larger group the total bill for a shuttle can climb rapidly. Here is another shuttle service
http://www.transportationmonteverde.com/ They quote $95 from the airport to Tamarindo for up to 5 passengers ($8 more for each extra passenger over that and $10 more for night service)
Also, the hotel she is staying at may offer their own discounted service for its guests or at least provide better info on transportation alternatives.
All of the above, was based on just a very quick search. Of course, she could do the same and might find some better deals, but this should give her a rough idea.
Here is an informative link to an article on the Liberia airport itself
http://www.costa-rica-travel-magazine.com/07-98-costa-rica-liberia-airport-01-03.htm. It doesn't say anything about what color the cabs are or duty free booze but does mention they have a bank.
One more link with even more detailed info on banks in the area
http://www.online-costarica.com/principal.html#Money_Talk. No mention of an ATM at the airport, but if they can't change money immediately upon arrival I'm sure whatever transportation service she uses will be more than happy to take her dollars.
The airport is relatively new, only recently earning international status, and is rapidly gaining in popularity for foreign visitors heading to the northern beaches. I wouldn't be surprised if additional services and amenities not mentioned here have recently been added.