While I agree that she could have done this better (in general, being more open to the other parties (where possible) in terms of a better deal for the UK), I think the part in bold is a tad harsh.
What is she supposed to do when the likes of the SNP (who admittedly have their duty to the Scottish who overwhelmingly voted to remain), Plaid Cymru (who pretty much gave the middle finger to the majority of the voters in Wales) and Lib Dem basically fight against Brexit at all costs and barely (if at all) provide anything in terms of negotiations to try and get the best deal?
What is she supposed to do when Labour, the main opposition, has been indecisive for the two years as well and have done very little in terms of negotiations, followed by Corbyn's temper tantrum after losing a no confidence vote against May and instructed Labour not to discuss anything with her?
What is she supposed to do when the Tories effectively started back stabbing each other and imploding because any deals made wasn't 'there ideal Brexit' (I admit that this is something May could have possibly sorted out, but even then you can't predict when something like this could happen)?
What is she supposed to do when many MP's from most parties simply didn't want anything to do with Brexit whatsoever and even attempting to lie about it (such as Owen Smith persistently lying that his constituency voted to remain in the EU)?
This is just internal to the UK. Put all these together and you get the main question.
How was May going to negotiate any form of deal that could possibly benefit the UK when she is sent to negotiate with the EU with her hands, feet, fingers, toes and wrinkled pussy tied by all parties (including her own)?
You also have to question whether those who rejected the deals actually had it 'in the best interests of the UK' or whether it was purely politically motivated ('I won't vote for this because it's the Tories etc).
Don't get me wrong. This is not intended to be a full defence of May and when she took over from Cameron, she knew what she was walking into, but for some to say that she's one of the worst PM's simply because of this (especially as we had a PM who went to war on the basis of 'a belief' and innocent people are now paying the price for it) is ridiculous.