A second referendum after an election is a meaningless position.
Let's just set out the process.
By mid-December, we need to have the Withdrawal Agreement sorted. That's because the EU need to then pass it through the European Parliament and then the Council of Ministers. The Withdrawal Agreement needs to ensure that the Good Friday Agreement is maintained.
By end of March, we need to have the Withdrawal Agreement agreed upon in Parliament.
Either of those things don't happen, we crash out of the EU with no transition period.
To call an election requires around 100 Tory MPs voting for one, alongside all the other opposition parties. They're more likely to have a leadership contest instead.
To sort out a referendum will, realistically, take months. Last one took about a year to organise, and the legislation left huge loopholes which we're seeing with the dubious shit Vote Leave were up to.
We could ask to extend the Article 50 period to beyond March. And that might possibly be agreed to by the EU if there were to be a referendum. But it'll come before an election and it'll be, in some shape or form, on a deal agreed by May.
So come March, should May not totally screw up, there'll be a vote. It'll be a vote on whether to crash out of the EU or not. And she'll likely need Labour votes to carry it through Parliament. So what is the Labour response? Policy at the moment is to reject any Tory deal put forward (that's what the tests mean). But that gives 'no deal', and Corbyn will be walking to make the same vote as Boris and Mogg and IDS. And Field and Stringer and Hoey. Saying, "we'd like an election first and then we'll hold a referendum once we've figured out our position on Brexit and negotiated it with the EU" may not cut much ice in the fallout of the consequences.