Hana Shalabi, whom Israeli military officials were holding for alleged terrorist activity, agreed to the deportation deal last week and ended a 44-day hunger strike.
"I hope you understand and respect my decision in ending my 44-day hunger strike. It's not because of weakness, but because of internal bleeding and medical complications," Shalabi said in a letter released by her lawyer Sunday.
She was being treated for dehydration and weight loss Sunday, but her medical complications were not life-threatening, said Dr. Yehyaa Khader at Gaza's al-Shifa Hospital.
Shalabi agreed to be deported to Gaza for three years, after which she will have the option of returning to her home in the West Bank, attorney Jawad Bulos said last week.
Shalabi's attorney said her hunger strike was aimed at protesting "administrative detention," a controversial practice that allows Israeli authorities to detain people indefinitely without formally charging them.
Addameer, a Palestinian group supporting Palestinian political prisoners, says such detention allows military commanders to detain people for as long as six months if they have concerns for public security, but the detention order can be indefinitely renewed.
Israeli authorities detained Shalabi in February, after the military said it had intelligence reports that she had resumed terrorist activity.
She began the hunger strike to protest her detention, her attorneys said, and she was transferred to an Israeli military hospital as her condition deteriorated.
Israeli government spokesman Mark Regev told CNN last month that a judge had ruled that Shalabi presented a danger.
"She is an activist in Islamic Jihad, an extreme terrorist organization, and the judges ruled that incarceration can continue," Regev said .
Islamic Jihad has been blamed for suicide bombings in Israel that have killed dozens. Both the United States and the European Union consider the group a terrorist organization.
The Israeli military said military courts approved Shalabi's detention "on the grounds that there was current and reliable information that Shalabi posed a specific and concrete threat, and that there was no alternative criminal procedure available to address this threat."
Her attorneys said Shalabi told them she was beaten, abused, blindfolded and interrogated, and placed in solitary confinement for the first week of her arrest.
Bulos said last week that Shalabi was in the prison ward by herself, drinking only water, and that authorities told her "she is not like Khader Adnan and no one will hear her case."
Khader Adnan is a Palestinian detainee who ended his 66-day hunger strike in February after the Israeli government said his sentence had been commuted and would not be renewed. He was told he would be freed in April "as long as no new significant material was presented against him," Israel's justice minister said last month.
The Palestinian Authority had called for Shalabi's release and for international intervention in the case.
Shalabi previously spent two years in administrative detention before being released in October 2011. She was among more than 1,000 Palestinian prisoners released from Israeli jails in exchange for Israeli soldier Gilad Shalit.
Addameer and Physicians for Human Rights-Israel criticized her deportation Sunday.
"Forcible transfer and conditioned release is not an alternative to Israel ending its practice of administrative detention. It is imperative to demand a permanent resolution to Israel's practice of arbitrary detention, in compliance with international humanitarian law," the groups said in a statement.
Also Sunday, Hassan Abed Rabo, a spokesman for the Palestinian ministry of prisoner affairs, accused Israeli prison authorities of beating more than 60 inmates who refused DNA tests at a southern Israel prison. He described the inmates as political prisoners.
Israeli police spokesman Micky Rosenfeld said reports of beatings at Nafha prison are "false claims."
