The two adults and one teenaged child later succumbed to their injuries.
Minutes later, she said, she came upon a gruesome, chaotic scene at an intersection near her home, with first responders running to help, a police officer performing chest compressions on one person and three other people lying on the ground.
Four members of the Canadian Muslim family were killed on Sunday when a pickup truck jumped the curb and ran them over in London, Ontario province, officials say.
Nathaniel Veltman, 20, was in custody facing four counts of first-degree murder.
Mayor Ed Holder called the deaths "an unspeakable tragedy".
The group that represents Muslims across Canada also expressed their grief and frustration.
Ontario Premier Doug Ford says justice must be served "for the horrific act of hatred" that occurred in London, Ont., on Sunday. They say he was wearing a body-armour-type vest at the time he was apprehended.
Four years ago, a skinny 27-year-old white supremacist burst into a Quebec City mosque and unleashed a hail of bullets on worshippers who were chatting after evening prayers, killing six men and seriously wounding five others.
Police Chief Steve Williams said relatives had asked no names be released but identified the four victims as a 74-year-old woman, a 46-year-old man, a 44-year-old woman and a 15-year-old girl.
Just prior to the attack, Alek Minassian posted on Facebook a reference to an online community of "involuntary celibates" whose sexual frustrations led them to embrace a misogynist ideology.
Police are in contact with the Royal Canadian Mounted Police about whether terrorism charges should be pursued, Waight said.
Zahid Khan, a family friend, said the three generations among the dead were a grandmother, father, mother and teenage daughter. "We are also here for the child who remains in hospital - our hearts go out to you, and you will be in our thoughts as you recover".
"An Islamophobic act of terror like this has no place in Canada", O'Toole said on Twitter.
"I was shaken up, thinking it was an erratic driver", Martin said.
"I can't get the sound of the screams out of my head", Martin said.
She later saw a flurry of emergency vehicles speed to the scene.