Shourd was smiling as she walked arm and arm with her mother, Nora Shourd, on the tarmac at the Oman airport.
"I am going to make sure that she now gets the care and attention she needs," Nora Shourd said in a statement. "I can only imagine how bittersweet her freedom must be for her, leaving Shane and Josh behind."
Shourd, 32, had been detained since 2009 when she and her two traveling companions, fiance Shane Bauer and friend Josh Fattal, were arrested and accused of espionage. They were picked up after allegedly crossing into Iran from Iraq in July 2009. Fattal and Bauer remain jailed in Iran.
Shourd was granted freedom after discovering a lump in her breast, but not before making a guarantee of $500,000 bail.
Shourd Thanks Ahmadinejad
Before leaving Iran, Shourd singled out President Mahmoud Ahmadinejad in a statement of gratitude on Iranian TV.
"I want to really offer my thanks to everyone in the world, all of the governments, all of the people that have been involved," said Shourd, 32. "And I especially, particularly want to address President Ahmadinejad, and all of the Iranian officials... and the religious leaders, and thank them for this humanitarian gesture.
"I'm grateful, and I'm very humbled by this moment," she said.
Family of Jailed Hikers Speak Out
The families of all three hikers released a statement saying that they "applaud the Iranian authorities for showing compassion in Sarah's case and again call on them to do the only right thing and release Shane and Josh immediately."
Laura Fattal, the mother of Josh Fattal, said that her only mission is to bring the two remaining hikers home.
"We believe in our hearts they [Iran] will have this compassion to release both kids and we hope as soon as possible."
Shane Fattal's brother said Ahmadinejad should bring the two jailed men with him to the United States on his upcoming trip to New York.
"We profoundly share in the joy of the Shourd family and we want nothing more than to have that for our families as well," Alex Fattal said. "It's really heartbreaking the fact that Josh and Shane are still not home."
Tehran's prosecutor offered little hope for the two jailed hikers, saying they will now be tried for spying. Newsweek reporter Maziar Bahari, who was held in the same prison last year, said Shourd likely left Iran with her own chilling warning.
"They tell you what you should do, what you should say, what you shouldn't say," Bahari said. "The revolutionary guards, they have agents all around the world and they can always harm you."
President Obama Asks Iran to Release Two More Hikers
President Obama said he was "very pleased" by Shourd's release, and called for the release of the other two hikers in a statement, saying they "have committed no crime."
"We remain hopeful that Iran will demonstrate renewed compassion by ensuring the return of Shane, Josh and all the other missing or detained Americans in Iran," Obama said.
The State Department said that the willingness to release Shourd proved Iran's ability to "resolve" all the hikers' cases.
Iranian officials, including Ahmadinejad, had announced last week that Shourd would be released on Sept. 11.
Officials in Iran's judiciary canceled Shourd's release Friday, but reversed themselves Sunday on the condition that her family post $500,000 bail, according to an Iranian prosecutor who spoke to Iran's IRNA news agency.
A "bank guarantee" for the bail had been given, Shafie told ABC News.
"The case inspector informed the Tehran prosecutor of a bank guarantee concerning the posting of bail and after the prosecutor's agreement, he issued the order for her freedom," the prosecutor's website said, according to PressTV Iran.
The report did not say who was responsible for the guarantee, but two U.S. officials told ABC News Iran had received "assurances" from the country of Oman concerning the bail money.
A senior U.S. official familiar with the negotiations told ABC News Monday that the U.S. government would not be contributing any cash for Shourd's release.
Lawyer: Shourd's Health is 'Very Weak'
Shourd faces trial for allegedly illegally crossing Iran's border, according to Iranian prosecutor Abbas Jafari Dowlatabadi.
"I think it's irrelevant whether they actually believe they have a case or not," Rudi Bakhtiar of the International Campaign for Human Rights in Iran told "Good Morning America" Monday. "I think what's important is they are going to push that case... It would make them seem weak if they turn around and say, at this point, 'Hey, we've been mistaken.'"
Shourd's release was inspired at least in part by her deteriorating health, a condition Shafie said he made clear to Iranian officials days before her release was first announced.
"I gave a letter to Tehran investigators, and I warned [them] about Sarah's situation, and that her health is very weak. They can hold them for up to a year for the investigation, but not more than a year if they haven't been given a proper trial," Shafie told ABC News through a translator last week.
On Aug. 10, the mothers of the hikers made another open plea to Iran's leaders, invoking the sacred time of Ramadan and Shourd's "serious medical condition."
"Sarah has a serious medical condition and we are gravely concerned for her physical and emotional welfare, for which Iran's leaders are responsible. We urgently call on the Iranian authorities to end her isolation and provide her with adequate care," the mothers said in a statement on a website dedicated to the hikers' release.
In an interview with "GMA" in May, Shourd's mother said she wasn't sure what she would do when finally reunited with her daughter.
"I think I'm just going to say ridiculously silly things," Nora Shourd said. "'I'm so glad to see you, sweetie. How are you? I love you.' You know, just ordinary stuff."
ABC News' Jason Stine, Kirit Radia, Sabrina Parise, Thea Trachtenberg, Kevin Dolak and The Associated Press contributed to this report.