Hillary Clinton is human, too. She just has a hard time showing it.
Clinton was always going to be the Democrat presidential nominee. The press was looking out for her and the DNC was doing all they could to stop any momentum obtained by Bernie Sanders. While many thought Clinton had the charm of a wet blanket, it never really mattered. She was going to win no matter what.
Clinton's lack of affability was also not going to be a problem against “low-energy” Jeb Bush, either. But against Trump, she was going to have a problem. Before voting began in Iowa, it became increasingly clear that Trump was going to be the Republican nominee. If Clinton was going to win against the bombastic billionaire businessman, she was going to have to show some charisma.
Unfortunately, charisma doesn't come naturally to Mrs. Clinton, so her speech writers had to write some in for her.
See her staff instruct Clinton to smile in emails leaked by WikiLeaks on the next page: