I dont follow the British internal squabbles too keenly, it's too complex and frankly they care plenty themselves, don't need my input. But what I'm picking up here and there is that she's breaking her promises because she's finding out there isn't much she can do to keep them, what with reality and all that. She's no Trump, as England isn't exactly a superpower. It still has the memory of being one in its system, and Theresa "Child of Regulus" May might just have been intoxicated on that memory a bit. On the other hand, children of Regulus don't tend to fall before they've properly risen, if they fall at all.
It may be that May is 'destroying [their] politics' as a columnist put it, but that she is not thereby destroying her command of the situation, which at this juncture is equatable with the will of the United Kingdom. Her will being all the forces that contribute it - a female PM must always be a mediator of great forces, she must always be a walking contradiction, an open treachery. That is the only reliable way for a woman to walk the path of exaltation by power, the alternative is a mere housemaid of economy with no sense for what's under the Sun.