Their sources indicate that her transformation will NOT take place in this installment of Ant-Man. Does that mean they'll leave it for a sequel? What's certain is The Wasp won't come out to play in this year's Ant-Man.
In other words, it's not that they know when she turns, but they know when she doesn't.
As to Ant-Man's bouts with Yellowjacket, it seems they'll come to blows two times in the movie. The first takes place in a suitcase. The second one "“ which is also the final battle "“ is in Scott Lang's daughter's room.
It sounds spectacular: "we’ll see both characters enlarge certain objects while they’re still shrunk, accidentally making a giant ant and, eventually, Thomas the Train, which crashes out of the bedroom, crushing a car on the street."
Cool, right?
Civil War: taking sides, costumes and who triggers the action

The source indicates Cap will be backed up by the Black Widow, Hawkeye, and Falcon, whereas War Machine, The Vision, and Ant-Man "“ yes, ANT-MAN!!! "“ side with Iron Man.
What a shocker to hear of Ant-Man in Civil War! But there's more: "expect to see Ant-Man take on the Giant-Man form in battle".
But where does that leave the Winter Soldier, Spider-Man, Scarlet Witch and the Black Panther?
