For anybody thinking Warren should be good-enough substitute for Bernie to Bernie fans: Kyle Kulinski (Secular Talk on YouTube) collected some differences between them
here.
She is not in favor of eliminating medical debt or all educational debt.
She was in favor of approving Ben Carson... then flipped under pressure.
She admitted that the DNC had rigged 2016 against Bernie... then flipped under pressure.
Speaking of 2016: she refused to officially endorse Bernie despite being in theory more like him than Hillary on policies, so that decision was some kind of machiavellian calculation, rather than a stance on policy principles. (Some say Hillary got her to do that by saying she'd appoint her to something if she won, but somebody more principled or less gullible & pressurable wouldn't have fallen for that.)
She's an
obstacle to universal single-payer medical coverage. Yes, she now claims to be for it, most of the time, but that's just another of her flips under pressure. Her original spiel, from before detecting how hard the wind was blowing that way, and which still does accidentally sneak out in bits & pieces from time to time, was wafflier than Waffle House on a Sunday morning, full of blather about how all of the Democrats' proposals are essentially the same and how the ones that are based on and framed in Republican talking points are just as good as long as they now come from "Democrats"... trying to sound like she might be in favor of whatever anybody listening might want.
She keeps voting for the always-increasing military budgets, including the latest one that shoveled even more money at it than Trump had asked for.
She takes donations from military contractors while saying practically nothing about changing any part of the Bush-Obama-Trump military behavior. (KK says she's also done "favors" for them, but doesn't specify what those were, beyond throwing lots of tax money back at them and staying silent on their neverending foreign intrusions, as stated above.)
She said at first that she'd refuse big-donor money like that for the primary season but accept it in the general election. This is inherently hypocritical already (because if you accept the principle against it, which is that it's a corrupting influence and a corrupt system, then taking it sometimes is openly participating in the corruption sometimes), but there's more: she then got caught sneaking big-donor money into her primary campaign budget too.
When she had an interview in which the interviewer mentioned the progressive movement's challenge against corrupt DINOs like Joe Manchin, she felt compelled to give a "spirited defense" of Manchin. (KK used this as an example of her adopting the language of party unity and bipartisanship rather than treating opponents as opponents who need to be defeated for the good of the country & people, but didn't give more examples.)
Finally, although she does have policy proposals that address certain aspects of the class struggle, KK says she doesn't push the subject as often or as forcefully or in as much of the right kind of elitists-vs-the-rest-of-us framing like Bernie does, so, no matter how good those proposals might be, she's not enough of an advocate for them or for the general principle driving them, helping to push the national conversation in the direction that would make such policies more likely to pass and their supporters more likely to get elected. (I can't really say I'm quite with him on this one; I'm sure one could find examples of her sounding weak & waffly or even evasive or contradictory to such ideas & framing on certain occasions, and I'm sure the opposite could be found too, but I can't say it goes one way or the other as a dominant trend of hers... other than by comparison to someone as all-out as Bernie is about it... but the comparison is still valid in a way... just mainly because Bernie is Bernie, rather than because Betty is Betty.)