score:2
I can't find a Costa Rican source for this, but according to TIMATIC, it is possible to transit without a visa if the onward flight is within twelve hours of the arrival.
Alternatively, the traveler is excluded from the visa requirement if she holds certain visas of other countries, including the EU. Her US visa won't help with this because it is a transit visa, but whatever documents she had to enable her to travel in Europe might.