Nancy Writebol arrived in a private plane equipped with a unique containment unit at Dobbins Air Force Base near Atlanta on Tuesday morning. She will join colleague Kent Brantly in a special isolation unit at Atlanta's Emory University Hospital, Xinhua reported citing US media reports.
SIM, the aid group with which Writebol serves, said she "remains in serious, but stable, condition".
Writebol was serving on a joint medical team in Liberia with Brantly of Samaritan's Purse, an international relief organisation, when they both contracted the virus.
Brantly was brought back by the same medical evacuation plane Aug 2 for treatment.
According to Samaritan's Purse, Brantly is "in good spirits" and his condition "is improving."