The whole idea, as Theresa May said, is to give her government a firm mandate to get on with it in the way she has said. Total independence from the EU, no membership of the Single Market or anything else, without all the Opposition (notably a certain Mr Farron) continuing to bleat about "this isn't the kind of Brexit people voted for". Effectively, in the way she has presented it, it's a second referendum on "what kind of Brexit".
The Lords are another issue... but if this kind of Brexit is in the Conservative manifesto, then it is something they should not refuse under the Salisbury convention.
She's pretty confident of another Conservative majority and then the argument will be "the people elected us KNOWING that this is what Brexit will be, so SHUT UP". And there is the attraction that the EU will know that too as we go into negotiations - if the Conservatives get another overall majority, she will have all the backing anyone could possibly want.
The convention in the EU is that you don't comment on national elections because they're a domestic matter. But as this election is so obviously bound up with Brexit, there have been EU politicians who couldn't resist the temptation to break the convention, and noises off from across the Channel are that this will be helpful for negotiation. They'll know where they stand, facing a British Prime Minister with the people's backing.
Of course she could lose. And then we'd be in a total pickle. But being over 20 percentage points ahead in the opinion polls at the moment, she thinks this is a chance worth taking.