Have we actually seen evidence of people not voting because they were sure she had it in the bag? I hear that thrown around but it doesn't seem like that overconfidence of the voting body should have played that much of a role in depressing the vote- afterall, by voting for her you 1) were part of a histotic first by electing a woman to president, 2) stuck it to the orange bad man, and 3) the vote is never certain, if you want someone or some legislation to succeed you have to vote.One of the reasons why Trump beat Hillary was because a lot of people were convinced that she was going to win and it was a widespread belief on both sides that Hillary Clinton had it "in the bag" right up until Election Night. Naturally, a lot of people who would've otherwise voted Democrat just stayed home.
While Clinton's sheer unlikable nature and the way Bernie was so fucked over in the primaries did go a long way in her 2016 defeat, the overconfidence of the Democratic voter base that year did play a role in her defeat as well.
I don't doubt that there were people who stayed at home disgusted by both candidates, but I don't think I've seen evidence that (large enough amounts) people just didn't vote because they thought it was a sure thing. It just seems like it downplays the fervor of her supporters, who were pretty adamant about their support.