Right now however, the lack of general election means she has no mandate to push through her entirely secretive manifesto where random policies pop up that no one has given her a mandate for such as grammar schools, foreign worker lists, increased public spending and a slow down in debt reduction and so on and so forth.
It is too restrictive to require the government to only implement policies in their manifesto as this would restrict the government from reacting to changing circumstances. Almost all the policy changes you mention are a reaction to the (hopefully short-term) uncertainty caused by Brexit. The policy on grammar schools was not mentioned in the last Conservative manifesto but was not ruled out by it either. It would not be practical to restrict government to only enact policies that were in their manifesto. Calling May a dictator is absurd.
I think your argument that the 52% who voted for Brexit don't agree on what form of Brexit they want ignores the fact that the Remain side were if anything more divided on their vision of what Remain would mean. Labour supporters would see the EU as a way of expanding workers rights whereas Conservative supporters would see it as a vote for expanding free trade. The opinion polls consistently ranked sovereignty and immigration as the top two reasons people voted for Brexit.