It seems possible that there wasn't much initial due diligence nor a working product at the beginning:
> Tim Draper, the venture capitalist, said Holmes, who was friends with his daughter growing up, is the first entrepreneur he knows who kept quiet about her business
From what I understand, Tim Draper, of DFJ Venture invested in Holmes when she was a Stanford student.
> DFJ, formerly known as Draper Fisher Jurvetson, became one of Theranos’ first investors. The firm doesn’t have a seat on the Theranos board, Jurvetson said.
“We wrote a $500,000 check before anyone else, but she’s been somewhat independent and has been going at it all on her own, so I don’t have the answer to your question,” Jurvetson said when asked whether DFJ would invest again.
It seems most likely to me that this investment was based on her personality and/or personal connection, rather than due to a technology breakthrough she had made at the time. If she had something at the time, then it's taken 11 years to get where they are now, which is not having any publishable research demonstrating the results. My guess based on the situation is that she was charismatic and asked for money to go start solving the problem, from scratch, and people gave her money because of her charisma and because they judged the problem sufficiently tractable. It seems unlikely that she had more than an idea while still in university.
It looks like DFJ has not participated in the most recent investing rounds (?)
http://www.mercurynews.com/michelle-quinn/ci_26147649/quinn-...
http://www.bloomberg.com/news/articles/2015-10-19/early-ther...