If she's elected president on Sunday, Europe may face the prospect of a French exit from the EU
What Sunday? Next elections are 2022.
Also that's not how the french system works. She won't be able to unilateraly leave the EU. And I don't see enough députés or senators back her to actually make that happen.
Most of them are cultivated people who will understand how bad it would be for France.
France is not a dictatorship. It's not like the president can just say that the country will be leaving the Union.