JFTR, May isn’t a head of state; she’s the head of government. The Queen is the head of state.
The queen is just a figurehead, with hardly any powers. May is, in reality, the head of the British government, therefore, head of state. Technicalities are worthless when practicalities matter more.
And, yeah, I know what you mean, but still, May is more important when it comes to the government in the UK.