Britain doesn't have to hold an election for another three years, but her Party (the Conservative Party) is way ahead in the polls, so why not strengthen their hold on parliament? That's got to be what they're thinking.
And the leader of the Labor Party, Jeremy Corbyn, is very weak.
Here's her announcement - https://youtu.be/4xr9-CkZZRk
and Corbyn's response - https://youtu.be/pIt1kHkTJ8I