Since Goldsmith, the Tories haven't even tried in London.
What they have done though is changed the election rules to tip the balance in their favour, and this alone might be enough to get them the result even with a candidate as woeful as her. Khan is currently on 33% and Hall on 32%. Under the old system, most of the Lib-Dem and pretty much all the Green votes would have transferred to Khan making it a non-contest.
All it needs is for Corbyn to run and take some Labour votes, and the Tories to stoke up some ULEZ angst in the areas outside the N and S Circular and Hall might get through.