She probably can't, because of the fixed term parliaments act. Not without a supermajority in the commons. Normally that would be impossible, but Corbyn is such a **** that he will probably support it.
Alternatively she could pass legislation to amend/suspend/repeal the act with a simple majority but the lords would likely tell her to piss off and stop playing silly buggers.
She might be quitting, more likely a "oh brexshit" statement.