"She was the mother of two small children and a humanitarian with the highest ethics and professionalism," HEAL Palestine, posted on its Facebook page.
"HEAL Palestine is more dedicated than ever to serving Gaza, in her honor. Ceasefire now," it added.
Her family issued a statement on Friday, saying they were told by government parties at the hospital where her body was taken that she was killed by mistake. Her killers, whose identity was not disclosed, had failed to identify the vehicle she was driving, they said.
Later on Friday, the Hamas-run interior ministry said it had launched an investigation into Hejazi's death, which it described in its statement as an "accident", without further details.
"That was a bigger shock .. How would an innocent soul be wasted and 90 bullets fired at her car just for mistaken identification?" the family said in a statement published by Palestinian media.
Reuters was not able to verify the number of bullets fired.
The incident highlights growing chaos and anarchy in Gaza almost a year into Israel's military offensive, which the Hamas-run government says has weakened the ability of its security services to police the streets.
Palestinians have complained of rampant theft, gangsters, and price-gouging merchants. Gaza has a population of 2.3 million people, most of whom have been internally displaced by the war, which has killed 41,500 of them, according to Gaza health authorities.
Israel and Hamas have been fighting since gunmen from the Palestinian militant group stormed into southern Israel on October 7, killing 1,200 people and capturing some 250 hostages, by Israeli tallies.