(CNN) -- When Barack Obama won the U.S. election four years ago, his Kenyan half sister Auma was with her family at their homestead, watching the historic occasion on television.
It was a night Auma Obama remembers well. "We had a lot of people visiting to watch with us," she says. "There was a lot of excitement because it had been such a tough race. There was a sense of relief that all the hard work had paid off."
Alongside Auma and her family was filmmaker Branwen Okpako, who was making a documentary about Auma, "The Education of Auma Obama, " which is being shown in London Tuesday to coincide with the U.S. election and as part of the Film Africa festival.
"I will never forget that period in their homestead," says Okpako. "It was indescribable. Imagine something like that is happening to your family, yet so far away."
Okpako, 43, a Nigerian-born filmmaker living in Germany, became friends with Auma when they were both film students in Berlin in the early 1990s.
"We were two of four African women studying at the film school at the time and we talked a lot about how the African continent was portrayed in film and how we wanted to change it," says Okpako.
Auma shares a father -- Barack Senior -- with her younger half brother, Barack. The pair did not meet until after their father died in 1982 and Barack got in touch with Auma to explore his Kenyan roots.
Okpako had the idea for a film about her friend Auma in the run-up to the 2008 election.
Auma recalls: "I wasn't particularly enthusiastic when Branwen first suggested the film, but I agreed because she is a friend and I trusted her. If it had been a stranger, I don't think I would have done it."
Okpako says Auma was initially reticent about the film because of the huge media interest in her family that came with Barack Obama's rise to prominence.
"It has put me in the limelight in a way that wouldn't have happened otherwise," says Auma. "I don't like talking about my family but it's great if it gives me the chance to talk about my work with deprived and underprivileged children."
Auma, who lives in Nairobi, traveled with Okpako to the family's homestead in the village of Kogelo, where her grandmother lives and Barack Senior is buried.
"We were sitting together for 10 days waiting for the election and reflecting how we got to this moment in time," says Okpako.
"We were reading the newspapers and reading the statistics, but of course we didn't know what was going to happen. It was intense and full of anticipation.
"The film deals with that moment in time when history was made, but also how they got to that moment."
She adds: "All the family was there, the grandmother, all the cousins. Once the result was known everybody in the village came into the compound to celebrate. There must have been hundreds of people there."
Auma Obama grew up in the family's homestead in Kogelo before moving to Germany where she spent 16 years as a journalist, broadcaster and studied for a PhD in German literature.
She then lived for a period in the United Kingdom before returning to Kenya, where she works now as a social worker and youth advocate.
The film is partly a fly-on-the-wall documentary about the family watching the 2008 election from their homestead, and partly uses interviews and old footage to tell the family's story.
Okpako traveled with Auma Obama to many significant places in her life to trace her story. She had hoped to interview Barack Obama for the film, but was unable to arrange time with the president.
"I thought it would be good to have him as a small character in a film about an African woman, but it wasn't possible," she said.
The president did, however, get to hear about the film when the cameraman's mother-in-law visited the White House with German chancellor Angela Merkel and told him about it.
"He asked for a copy and we sent it, but I don't know if he has watched it," says Okpako. "I think it would be interesting for him to see what his Kenyan family was doing that day."
"The Education of Auma Obama" will be shown in London on this year's election day, Tuesday, November 6, as part of the Film Africa festival, and Okpako will be there for a question and answer session with the audience.
Auma says she has to work on election day, but she will still be watching events unfold.
"I follow my brother's career as closely as any sibling would," she says.
"It's important for me to know whether or not he is happy in his job," she adds. "He makes me very proud because he has a tough job and does it 100% to his ability."
The film premiered at last year's Toronto International Film Festival and has won awards at the PanAfrican Film Festival in Los Angeles and the Africa International Film Festival in Lagos.