Some former hostages question whether the family should remain silent, saying pressure campaigns can work.
Ms. Zaghari-Ratcliffe, the British-Iranian charity worker held for six years in Tehran, said “freedom will never be complete” until all detainees were allowed to leave.
The arrest and detention of the British-Iranian charity worker in 2016 roiled relations between Britain and Iran and was denounced by rights groups.
Aras Amiri, an arts worker employed by the British Council, was arrested in March 2018 on espionage charges. She was acquitted in August and flew back to Britain earlier this week.
The British-Iranian woman has been detained in Tehran for five years on charges of plotting to overthrow the government, accusations that her family and supporters say are baseless.
Britain’s stance on the case of Nazanin Zaghari-Ratcliffe, who awaits trial in Tehran, has drawn criticism as it weighs its international role outside the European Union.
Iranian state media said the scholar, Kylie Moore-Gilbert, was released in exchange for the return to Iran of three Iranian citizens, described as businessmen who had been held abroad.
Nazanin Zaghari-Ratcliffe is already serving a prison sentence after being accused of plotting to overthrow Iran’s government. The case has strained already fraught ties between Britain and Iran.