She's had two chances at it, blown them both when the prevailing opinion going in was both times it was her race to win. Obama she can be forgiven for losing to him. Trump, even though she won the popular vote, she still made too many campaign mistakes along the way. The reality is, that there is a large enough portion of the voting base that just do not like her, and the Dems would do well to avoid her if at all possible. Her running could once again energize enough of the voters to give even Trump a chance (seems unlikely now, but then again it seemed unlikely going into the election that she could lose to him at all).
The Dems would do well to avoid her like the plague, unless they really have no one else.
This article does not paint a pretty picture for the Dems, so maybe Hillary is the only choice.
http://www.vanityfair.com/news/2017/06/no-one-likes-prospective-democrat-2020-candidates