She'd be a very successful candidate no doubt, if the DNC allowed it. You've seen how they did Bernie and he's an old white guy. I can't imagine them going for AOC. They're a fundamentally conservative organisation that exists to vet candidates and prevent anyone with the will to make "actual change" from being in a position to.
Also, they've argued in court that they are not a democratic organisation. They can block nominations entirely unilaterally, to one of the only two parties that can realistically field a presidential candidate. The other party is much more openly corrupt, which is a genuine achievement.
The US electoral system is entirely captured by corporate interests.
If AOC gets more votes than their conservative candidate in the swing states they might grudgingly take her. She likely would not get more votes because the Repubs have been on a propaganda campaign to discredit her since forever.
They are a corporate machine with a lot of the same donors as Republicans. Their job is to provide a nominal resistance to the oligarchy, not actually win, govern, or fix things. That's why they don't want Bernie who is not on board with their mission. He was so popular his ideas dominated the primaries, so the DNC pulled out all the stops to keep him from winning, because it would've been very hard to maintain their soft obstructionism with him pushing on so many issues from the bully pulpit.
This is part of why I think you actually should vote for the Dem candidate as long as they're not the raging fascist that Trump is - they don't care about your protest vote or whatever. They will just lose, shrug their shoulders and start fund-raising for the next season where they will continue to be the only viable option because of deeply entrenched structural obstacles to any alternative.
As the Nation is now we'd have to spend a term preparing everyone for it. Her running would realistically begin within weeks after the office is occupied. Lightly, yes, though running still.