In short, the opposition called a vote on fracking, which is supported by Truss' "pro growth" government, but was opposed in the conservative manifesto. The government declared that anyone who voted against the government (and for what they promised to their constituents when they were elected) would be kicked out of the party. MPs who then tried to vote against the government were reportedly manhandled and assaulted to force them to vote with the government.
There is a whole load of other chaos that happened in the last 24hrs that was just ultimately impossible to recover from.
I think the last 24hr has just proved even to her final supporters that she is completely incapable of leading a government.