Gabriella was living with her grandparents in Tehran and visiting her mother in prison in an attempt to minimise the trauma inflicted upon the family, while her father, Richard Ratcliffe, campaigned for his wife's release.
"This should now be the tipping point - the Iranian authorities should finally do the right thing, by releasing Nazanin and allowing her to return home to Richard and Gabriella in the United Kingdom".
Her family and the Foundation, a charity organization that operates independently of Thomson Reuters and Reuters News, deny the charge.
At a press conference on Friday, Richard Ratcliffe told reporters: "It's a happy day, but it's very tough for Nazanin".
But Ratcliffe said it was a bittersweet moment as his wife was "distraught" at the departure of her daughter, who she has seen regularly during her detention on sedition charges.
"It was a hard goodbye for Nazanin and all her family, but let us hope this homecoming unlocks another", Mr Ratcliffe said.
She called on the British government to settle the £400m debt it owes Iran and added: "I have now dealt with three Prime Ministers, four foreign secretaries, three ministers for the Middle East - every single one has looked me in the eye and said it's nothing to do with debt between us and Iran".
In a letter smuggled out of Tehran prison and published by the Centre for Human Rights in Iran last week, Zaghari-Ratcliffe wrote: "In the near future my baby will leave me to go with her father and start school in the UK".
But Mr Ratcliffe said since announcing he was running for his party's leadership, Mr Johnson had been "kept at arms length" by advisors.
- September 9 2016 - Mr Ratcliffe says his wife has been jailed for five years following a conviction on unspecified "national security-related" offences- a sentence he describes as "a punishment without a crime".
Her ability to speak English is severely diminished, and she will have to relearn how to communicate with her father, said a family statement. "I don't know what will be allowed or what will be possible, but it would be great for her to be able to Skype her mother sometime".
"Those brief minutes might be the shortest of cuddles, but without doubt the most attractive and uplifting cuddles in the whole world", she wrote.
Last month, Prime Minister Boris Johnson called for the release of Mrs. Zaghari-Ratcliffe during a meeting with Iran's president.
The family's MP, Labour's Tulip Siddiq, said Gabriella's parents have made a decision that "no family" should have to make.
"Iran must end their hostage diplomacy and release my innocent constituent".
Speaking in the Commons, Ms Siddiq previously said she was concerned about Mrs Zaghari-Ratcliffe's physical and mental health. "Britain should also solve its long running debt issue with Iran".
She said: "Most importantly, I am Gabriella's MP".