After reading this Washington Post's article on Obama's strategy, I think it's more accurate to say that he won than to say that she lost. And with a race this close, it's easy to look back and say this thing, this one thing was what cost her the race, but it could have been anything. I could have been the war. It could have been sexism. It could have been strategy, or bad advice, or Bill, or it might have been the jacket she wore to that one debate that one time.
Personally, I think part of the problem was that she's never actually run a strongly contested election. She's never had to come from behind, and she's never had to fight for every single damn vote. From the beginning, she apparently thought the campaign was going to be a walk, and when it wasn't, she didn't adapt to the changing circumstances.
Which, coincidentally, is why I've never bought the "I'm the stronger candidate" spin. By definition, the strong candidate is the one who wins the most votes, and that wasn't her.
Yes, if you count elections which everyone said would never count, and you don't count caucuses, which everyone agreed would, and you tweak the numbers a bit here and there, then she won the popular vote. Which isn't how the nomination is decided. But by any objective standard, more people voted for him than for her. And by every standard, objective or subjective, he has the majority of delegates.
I understand how she feels. I've lost a lot of close games in my life (Not when I play Scrabble with Christie. She always kicks my ass decidedly.) but I learned a long time ago that when the other team outplays you, and the game is over, you walk across the field, shake hands, mutter "good game" through clenched teeth, and you save the "we wuz robbed!" speech for the ride home.
If she really wants to take the fight to the convention, she has to convince 66 superdelegates who have already pledged for Obama to switch to her and convince all of the uncommitted superdelegates that they need to override the voters and give the nomination to her. There are a number of reasons that's not going to happen, not the least of which is what it would do to the future of the Democratic party. Obama has brought a ton of new, engaged, hopeful voters to the party, and to disillusion them to harshly would probably sour them for life on politics.