Warren is barely to the right of Sanders. She's a good deal more hawkish.
I wouldn't say that. I'd say that both Sanders and Warren barely spend any time talking about foreign policy. To the extent they do talk about it though, sure, Sanders is to the left of Warren, but they're both to the left of both Obama and the median Democratic Senator. E.g., Warren voted against arming Syrian rebels a few years ago, and voted against selling arms to the Saudis last year, both votes which got the support of about half the Dems in the Senate. And both Sanders and Warren support the US attacking IS in Iraq and Syria (as does the entire DC establishment, of course), so it's not like either is any kind of uber-peacenik.
Warren definitely isn't "to the left" of Obama on foreign policy (assuming "left" vs. "right" on foreign policy is isolationist vs. interventionist). For example, she often criticized the Obama administration for not being pro-Israel enough and was probably the biggest Israel booster in the Democratic Senate caucus after Schumer. She definitely doesn't prioritize foreign affairs the way some Democrats do (it's not her area of expertise), but she is undoubtedly a hawk within the bounds of the Democratic field and quite far from Sanders on the topic. Does that matter? Maybe not.
She is different from Sanders in other key ways also, including key ways that Sanders used as wedges against Clinton. She's a free trader rather than a protectionist, and she's strongly in favor of gun control when Sanders was opposed. Those were both issues where Sanders endeared himself to lower-middle class white people in the Midwest, Plains and Appalachia but where Warren would struggle to maintain the same message.
Maybe most importantly, Warren is a professor and intellectual and not very good at bringing her arguments down to voters' levels, something Sanders excelled at. If the 2020 primaries are all about "kill the banks," she'd be fine as that's her specialty, but otherwise she is much more Clinton than Sanders in terms of wonkishness vs. ability to connect to voters.
