She served a full four year sentence, which began in July 2013, for her work on an orphanage with former Christian prisoner Saeed Abedini. She was charged with "acting against national security".
During her time in prison she went on hunger strike in response to authorities not allowing her medical treatment.
Maryam is said to suffer from heart disease while MEC says harsh prison conditions have also resulted in her suffering from depression.
The charity is calling on Christians to pray for Maryam.
In a statement it said: "[Pray] that the Lord will strengthen Maryam mentally and physically, that Maryam will receive the medical attention she needs.
"For a joyful reunion with family, and that Maryam will adjust well to ordinary life after her long prison sentence.
"Pray that those responsible for the persecution of Christians in Iran will love mercy, act justly, learn about Jesus and choose to follow Him."