Yeah, she can win, if Trump and Clinton dropped out of the race. However, Gary Johnson would probably crush her in a head-to-head race, as Stein is viewed very unfavorably, especially after her 9-11 comments.
Anyways, if Trump and Clinton remain in the race, the 3rd parties are still in trouble.
In this election, we have an interesting predicament: to any rational person, neither Donald Trump or Hillary Clinton is remotely qualified to be President. Mr. Trump has no prior experience and advocates policies directly contrary to the U.S. Constitution while Mrs. Clinton is a pathological liar who is only being kept out of prison by her name. Either Jill Stein or Gary Johnson would be by far preferable to either of these two.
Unfortunately, it won't happen. The American electorate as a whole cares far more about name-branding than they do about real issues. Both Mr. Trump and Mrs. Clinton are political "rock stars" to their respective electorates, Democrats in particular. Trying to get a Democrat to vote for someone other than Mrs. Clinton is like trying to get a 16-year old fan girl to abandon Justin Bieber. It doesn't matter if there are countless other options with more talent, that's their "person" and they're going to stick with them.
Americans are treating this election like a reality TV show. I had held out hope that perhaps the sheer awfulness of the candidates might snap us out of it, but it's not going to happen. In all likelihood Mrs. Clinton will be elected and we'll continue to expand the tyrannical central government and enslave our children to an unsustainable national debt.
There are just two choices when it comes to voting in an American election, Republican or Democrat. The other parties have absolutely no chance of winning, and are wasting millions upon millions of dollars and everybody's time by pretending that they stand a chance. Two-party systems perpetuate themselves by having the party in power and the official opposition, and people often don't see a need for a third point of view.
The Green Party's candidate, Jill Stein, has a zero chance of defeating either primary candidate in the general election. Not only has the Green Party proven to be utterly ineffective in every single major political election, its very existence is a threat to those whom believe in democratic principles. By promising an "alternative candidate" to those which conform to the traditional right and left, the Green Party leads its constituents into a false sense of security. Any vote for Jill Stein effectively negates a vote for (most likely) the Democratic Party and Hillary Clinton, and further advances the monster that is Donald Trump, therefore setting back even further the principles upon which they stand. Jill Stein could be anyone, yet in this simple game of numbers, the Green Party loses, every single time.
There are many people who have not heard of Jill Stein. Although there are many people who currently are undecided on who they will vote for and they are still hoping someone else will enter the election, they simply haven't heard of Jill Stein. Unless Stein has funding and can effectively reach out to all 50 states to make her presence be heard, she does not stand a chance in winning the presidential election.
Recent polls indicate that Jill Stein's support at 5%, too low to partiipate in presidential debates. Her plan to win is to get the millions of young voters to vote for her because her policies would appeal to Sanders voters. This logic would make more sense if Bernie Sanders had not endorsed Hillary Clinton. He did endorse Clinton and is actively campaigning for her election. Stein will probably get the votes of the diehard Sanders supporters, but they are too few to make a difference. Jill Stein has no chance to win.