Of course she should and will resign, but I suspect she won't do it yet.
Labour are talking as if they have "won", which of course they haven't; polling a smaller share of the vote overall and winning less seats. They've done much better than expected of course, but have still not done as well as the conservatives.
So it would be entirely wrong to hand power to a party which less people voted for, and which has substantially less seats than your own. That's why I don't think May will step dowm just yet. But certainly her position in the medium term is untenable.
She ran the worst campaign in living memory, perhaps ever, and showed she is totally unsuited to political leadership, with a combination of shocking decision-making and terrible presentation. Nought out of 10.
However, she was basically offering the country a sludge brown carrot & kale smoothy, healthy and good for your teeth. Whilst Corbyn was driving around in his ice cream van offering free 99s. Unsurprisingly a public starved of goodies for the past 6 austere years, ran after the ice cream van.
When you consider this, i.e. the worst Tory campaign EVER, and Labours seemingly endless freebies, it's perhaps surprising Labour did not win. Moreover, had the Tories ran a better campaign, Labour would have obviously not done so well as they did. So the conclusion has to be that the Labour message has to change, or they will continue to be a party of protest. Sufficient numbers of people are not persuaded by the current Labour leadership.