Reyashi, who belonged to the Brigades of Izel Dein Al Qassam, the armed wing of Hamas, blew herself up at an Israeli army checkpoint, wounding 10 people in addition to the four dead.
Reyashi is the first Palestinian woman from Gaza to carry out a suicide attack. Sheikh Ahmed Yassin, Hamas' spiritual leader, told reporters that sending a woman on such a mission was one of Hamas' tactics.
"The current complicated Israeli security measures at checkpoints and roadblocks make it difficult for men to reach soldiers and settlers. Hamas saw that a woman could reach them and carry out a successful attack," said Yassin.
Reyashi's body was returned by Israel to the Palestinian side, and was picked up by a Palestinian ambulance on Wednesday night. On Thursday morning a procession of relatives, Hamas members and militants brought a coffin to Shiffa Hospital, placed Reyashi into it and carried her to Gaza City's main mosque for final prayers before taking her for burial.
Twenty men carried the coffin, wrapped in a green flag on which was written, "There is no God but Allah," while about 100 people waving green flags chanted slogans and fired rifles into the air.
"What Reem al-Reyashi did was not a shame for Palestinians, it was a great honor for every man and woman fighting the Zionist occupation," said Ahmed, a 23-year-old Palestinian wearing a black mask and waving a large green Hamas flag.
Reyashi's 24-year-old husband, Zeyad Awad, said he had mixed feelings of happiness and sorrow, adding, "I'm happy because she is a shahida (a martyr) and I'm sad because I've lost my wife and my two children are motherless."
Yousef Awad, Zeyad's brother, said his brother had been unemployed for several years. He, his wife and two young children had moved several months ago to a rented flat near the beach in southern Gaza City.
"Zeyad and Reem's father, who went to the Hajj (pilgrimage) in Saudi Arabia, had a fight several months ago, and then Zeyad decided to rent a new apartment and live with his family in southern Gaza," said Yousef.
Yousef said his family was shocked to hear of the suicide attack. "We are quite a peaceful family, and we are against anything that opposes peace," he said.
Yousef Awad denied that his brother Zeyad was also a Hamas activist, adding, "I have never heard or noticed that Zeyad was a Hamas member. When he heard about his wife's death he cried and said Allah bless her spirit."
Sheikh Youssef Al-Qaradawi, an expert in Islamic law, said that from a religious point of view suicide bombings are considered heroic deeds and one of the greatest forms of Jihad (holy war).
Al Qaradawi added that all Muslims must fight against Israeli occupation, and that women have to play a role in that resistance, saying, "sending a woman to serve such a case in not forbidden, because women can get where men cannot."
Other Islamic scholars disagree, saying there is no justification in claiming innocent lives or in suicide.
In his book "Islam under Siege," American University professor Akbar Ahmed writes, "There is no reflection of God as Beneficent and Merciful in killing innocent civilians."
In a videotape sent to news agencies, Reyashi wore a black long-sleeve dress and black headscarf, with a green strip across her forehead proclaiming, "There is no God but Allah."
She was smiling as she read from a paper, explaining why she intended to carry out a suicide bombing attack. She was holding an AK47 assault rifle.
"I will carry out this joint attack with our brothers from Al Aqsa Martyrs Brigades in revenge against the enemies of humanity who kill and destroy in Rafah, in Nablus and in all the Palestinian territories," she said.
A joint leaflet signed by Hamas and Fatah armed wing immediately claimed responsibility for the attack.
"The fire of revenge will never be extinguished. It will remain burning, day after day, until those villain enemies are burnt and leave our land. It was a dream for me to carry out this operation," said Reyashi.
Reyashi is the seventh Palestinian woman to kill herself in a bomb attack against Israel, and the first from Gaza. Six women from the West Bank carried out similar attacks in the past two years.
Um Husam, a 32-year-old Palestinian mother of four, slammed Reem al-Reyashi's deed, saying, "Islam does not order us to die and leave our children.
"Allah doesn't take us to paradise if we kill ourselves and leave our children without anyone to take care of them. Taking care of our kids would of course take every Muslim mother to paradise without such an attack," she added.