The nine other members of Silsby's team, most of them linked to a Baptist church in Idaho, were released earlier but she was held the longest because she organised the venture and prosecutors said she knew that she did not have the proper authorisation to take the children out of Haiti.
Silsby, 40, returned to her cell briefly to retrieve her belongings after Monday's ruling, before quickly heading to the Port-au-Prince airport.
Silsby's group were arrested while attempting to bus 33 children from Haiti to the Dominican Republic.
Eight members of the other group were released in February after a judge ruled they had not knowingly engaged in any crime.
The ninth member, Charisa Coulter, Silsby's friend and former nanny, was released in March.
Critics say that the entire incident has been a distraction from the plight of more than a million Haitians battling to pick up the pieces after the quake.
Highlighting their continuing struggle on Monday, some 1,000 protesters marched to the collapsed national palace to demonstrate against Rene Preval, Haiti's president.
The protesters accused Preval of failing to help the estimated 1.3 million people displaced by the quake. They also criticised him for seeking to remain in office for three months after his term, if polls cannot be held by November.
Tens of thousands more watched from the plastic-tarp-covered plots where they have lived since the earthquake struck on January 12.