Her supporters wouldn't vote for Trump, they've been brainwashed to think that he and all Republicans are devils. The worst thing Stein could do is drop out. Her supporters would convince themselves that a war isn't really a war if a liberal Democrat starts it and will vote for Hillary. Hillary already has most of the Sandersbots on board in spite of all the revelations about her yukking it up and backslapping with Goldman Sachs thanks to his endorsement.
Jill Stein thinks Bernie Sanders is too conservative.
That says all that one needs to know about her.