No doubting it was a difficult brief. However, in the infinite multiverse there is a version of reality where Ms May did prevail. Success was always possible in our reality but Ms May chose (i.e. was not forced) to act in a way that made this a non-starter.
1. She was a "Remainer", so how likely was she to be able to deliver Brexit?
2. She surrounded herself with "Remainer" advisers and a predominantly "Remainer" cabinet.
3. She got through 3 Secretaries of State for Brexit - this should not be possible in a closed issue.
4. Her third Brexit Secretary resigned after Ms May agreed the terms of a Withdrawal Agreement with the EU that he was largely unaware of. Why would Ms May adopt such a despotic approach to negotiation in a parliamentary democracy? Could it be it was because she was not intending to act democratically (see point 1)?
5. She agreed terms of a Withdrawal Agreement in secret, surely knowing that it would never receive majority support. This suggests she is utterly out of touch with her electorate and her party.
6. She took "no-deal" off the table. Even the weakest negotiator will tell you that, if you give away your currency of negotiation, you will not get a deal. Ms May was obviously under the impression she was playing "happy families", rather than poker.
It did not have to be the way it is ended up. Whilst I do not discount the very real difficulties faced when negotiating with 650 loose-lipped and self-serving idiots telegraphing your every move, Ms May could have made a better job of it. She is rightly being held accountable for that.