Attar turned heads in the head-to-toe outfit she patched together with her mother to race in the 800 metres at the 2012 London Games, where she was one of the first Saudi women Olympians.
This time Attar, now 23, will take on the gruelling 42 kilometer (26 mile) marathon race in Rio, where four Saudi women will take part.
The women and seven Saudi men arrived in Rio on Monday, but were kept away from prying media.
Along with Attar, they are judoka Wujud Fahmi, fencer Lubna al-Omair and 100m runner Cariman Abu al-Jadail.
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None qualified directly for their competition, but will take part with special invitations from the International Olympic Committee.
Attar has no regrets and no doubts about running in London and Rio.
"I was going for the women in Saudi Arabia, for all the young girls to have someone in the Olympics representing them, giving them a picture of something they could one day strive for," she said in a recent article for the Like The Wind runners' magazine.
Taking part in sport is not easy for Saudi women and finding women to go to the London Olympics was a challenge. Someone knew of the half-Saudi girl in California who liked running and so an invitation was made.
"My mom and I pieced together an outfit: a long-sleeve shirt, full-length running tights, and a head cover we found online," Attar told Marie-Claire magazine.
"I was proud to wear the uniform and liked that wearing the appropriate dress connected me to Saudi girls who want to run and have to be covered while they do it."
Attar and her family have also noticed change in Saudi Arabia since the London Games.
Her father, Amer Attar, told the Washington Post how on a 2011 visit, when his daughter wanted to go on a run, he gave her a boyish "cap and warmup pants" and drove beside her.
Last year, he saw men and women running together in Jeddah.
"I even saw a guy with his, I think, looked like his wife, and they were holding hands and running together. And she was wearing the abaya, and she was covered up, but they were actually running."
President Thomas Bach said "a commitment to 'non-discrimination' will be mandatory for all countries hoping to bid for the Olympics in the future".