First off, it's not a theory: a vote not cast for Hillary is a vote for Trump. Period.
Hillary is a strong supporter of health care: she brought the issue to the fore years ago where it remained.
Women's rights: she's been a champion of equal pay and other issues (Planned Parenthood) for decades.
African-Americans overwhelmingly support her. Do you know why?
Minimum wage: $12. Not as high as Bern, but a large improvement.
Gun control: a decades' long supporter of toughening laws.
Immigration: supporter of Obama.
Education: platform calls for free community college; debt-free public university attendance through $2500/year credit.
So, I don't know what you mean about her progressive ideas and credentials. Not as far as Bern, right, but a MASSIVE, MASSIVE difference from Trump.
Please, read this and learn a bit about her: http://www.pbs.org/newshour/updates/hillary-clinton-believe-candidate-stands-10-issues/