Her biggest problem is likability. At least 45% of population just do not like her no matter what. Get it? Her disapproval number remains 45% consistently from the day one she said to run for President. 45%! that is the highest disapproval rating in American political history. No one won Presidency with that disapproval rating. She really runs aginst history and conventional widom here.
Everyone has his or her disliked person in life. A co-worker or a classmate or a neighbor or a friend's friend or even a remote family member. Try to picture that "you disliked or abhored person no matter what" person running for US President now, can you give your vote to that person regardless of how you feel about him or her? Can you?
That is insurmountable!!
Take myself for example. I often found myself turning away from TV screen whenever Hillary is on. I am GOP person and vote every time for GOP candidate at all levels: federal, state and county. I do not know if I would vote for Hillary even if she was GOP!