There are about a million articles right now trying to answer that question. Let me sum it up for you with my thought. She ran a horrible campaign, period, end of sentence.

How was it horrible?
1) She ignored caucus states, seemed to have no idea delegates were apportioned
2) She overpaid staff, overpaid for events, blazed through money
3) Wrong message, wrong message, wrong message
4) 1-3 Made every other mistake people will point to possible

That is about it. Yes Bill Clinton did not help, but she did not lose the race because of him.