Heather Heyer, 32, was protesting against a white nationalist rally in the Southern college town in Virginia on Saturday.
The “Unite the Right” rally included members of the Ku Klux Klan and neo-Nazis who had descended on the town to protest the removal of a statue of Confederate general Robert E. Lee.
Ms Heyer was killed when a man drove a car into the crowd – 19 people were injured and five critically.
James Alex Fields, 20, was arrested on suspicion of murder shortly after allegedly fleeing the scene of the crash and has been charged with second-degree murder.
Ms Heyer’s mother Susan Bro spoke at the vigil and said she did not want her daughter to have died in vain.
Mrs Bro said: “Remember in your heart: If you’re not outraged, you’re not paying attention.”
“And I want you to pay attention, find what’s wrong, don’t ignore it, don’t look the other way. You make a point to look at it and say to yourself, ‘What can I do to make a difference?’ and that’s how you’re going to make my child’s death worthwhile.
“I’d rather have my child, but by golly, if I gotta give her up, we’re going to make it count.
“They tried to kill my child to shut her up. Well, guess what? You just magnified her.”
Ms Heyer’s grandfather, father, cousins and coworkers also spoke at the memorial service, recalling funny stories and sharing memories.
Ms Heyer’s grandfather, Elwood Shrader, said: “In earlier years, she wanted fairness, she wanted justice, she wanted everyone to get equal respect.”
Attendees of the vigil were asked to wear purple, Ms Heyer’s favourite colour.
Also killed on Saturday were two Virginia State Police troopers Berke M.M. Bates and H. Jay Cullen.
The troopers were aboard a helicopter providing video of the rally before it broke off to support a motorcade for Virginia governor Terry McAuliffe.
The helicopter crashed outside Charlottesville and an investigation is ongoing.