I wouldnt say she was particularly bad for the simple reason she did absolutely nothing though. She will be nothing more than an insignificant footnote in this island story.
While she had the potential to be so, her failure to secure a majority in the 2017 election meant that Brexit was able to swallow the governments agenda with a speaker and parliament quite happy to betray her. She was therefore unable to do much at all.
There was never anything that suggested she'd be a good Prime Minister. She was a knee-jerk right-winger whose only attribute had been longevity in an important post. She didn't do anything special in the Home Office and presided over a series of (perhaps inevitable) ****-ups.
As Prime Minister, her response was to be static. Her first speech on the steps of Downing Street was interesting - it could've shown a new direction and a real willingness to tackle major social issues in Britain. In the end, she achieved virtually none of it - she retreated, she controlled government output with a level of utter paranoia and wanted to be in control of it all - while simultaneously being a block on everything.
On Brexit, she not only created huge uncertainty over the direction of travel for Britain, she helped create a divisive post-referendum atmosphere where society became (and continues to be) seen through the lens of leavers and remainers. There was no attempt to unite the country, to bring remainers along - she clearly accepted the argument that seizing the leave vote would benefit the Conservative Party and her attitude to everyone else was '**** 'em'. Which might be fine electorally (indeed, it served her well) but solidified opposition too (hence why Corbyn in 2017 did relatively well too) - and made Britain a less cohesive society.
I'm sure she's perfectly nice to know, but as a politician she was deeply flawed in a very obvious way - and instead of overcoming her flaws, her actions just made them more and more apparent.
I do actually think she was quite honest as a politician. There was no pretence there, no razzmatazz. It's just that she didn't have much else. Potentially a whiff of the Gordon Brown there.