I don't think anyone is expecting saints, but she failed to spot an important part, indeed a legal part of a process not being completed, a part that she was ultimately responsible for. It doesn't matter who she delegated the fine details & work to, she should have checked that all due processes were completed. Was this just a single error of judgement, or is this likely to happen again? That's what some of us would like to understand, especially given her important role in government. If there is any suggestion, any at all, that delegating and not properly overseeing due processes is a habit, then her position absolutely should be called into question.
And all of this notwithstanding, there is still the matter of optics on this. Even if this was just one unfortunate slip, it has now given the opposition parties leverage against the government. They will not let go of this, and if she makes a mess of the upcoming budget and associated policies, it will be the hill that the government could fall on. And Labour are starting to make a habit of giving the opposition scoring points, which will further their position going forwards and make it easier for other parties to gain ground in the opinion polls. She needs to knock the budget statement out of the park in a few weeks, otherwise Labour could be in serious trouble.