Nevada often gets less attention than Iowa or New Hampshire, but I expect it could be the closest of the first four states.
So, Warren is positioned to potentially win all of IA, NH, and NV. Well, that would be a wrap if she manages it.
She'd definitely be in good shape, but she'd need to get at least 15% in SC, and preferably keep Biden's margin down to 15-20 or so.
If Warren wins both Iowa and New Hampshire, she and Biden would be the only candidates still seriously in the race by South Carolina. She should be getting 30% or so at least at that point, but it might be 60 Biden - 30 Warren - 10 for the field (although I think in that scenario it would look more than 50 - 40 - 10 as I don't think black voters are that loyal to Biden over Warren, especially in the context of Warren as the clear frontrunner). I don't think getting trampled in South Carolina dooms her, though; the black vote is very important but not dispositive in determining the Democratic nomination, and both Clinton and Obama had other strong bases that Biden lacks (e.g., I can't see Biden winning the Mid-Atlantic states at that point, as Clinton did, or the rural West, as Obama did).