From WTF Facts
A Kenyan elite runner passes water to a dehydrated disabled Chinese runner who was suffering. This slowed her time. She came in 2nd in the race not only costing her the win but also the $10,000 cash prize. It's not all about winning.
A blog post called What It’s All About said the following:
During the 2010 Zheng-Kai marathon Jacqueline Nyetipei Kiplimo from Kenya saw a Chinese elite disable athlete struggling to drink water. She ran with him from the 10km to the 38km mark aiding him through all the water stations. This slowed her time — she came in 2nd in the race — not only costing her the win but also the $10,000 cash prize.
Wikipedia has a paragraph on the marathon, so I think the marathon itself exists.
I came across a unrelated news article about Jacqueline Nyetipei Kiplimo, so she also is real. I don't know if she's the same person as the person in the photograph.
I came across http://www.malimwengu.com/africa/sports/i-have-never-regretted-helping-the-man-i-did-it-to-touch-someone-s-heart , but I don't think it's a reliable source.
Did this incident happen?