Holly Hunter first jumped into the superhero movie genre as the voice of Helen Parr, a.k.a. Elastigirl, in 2004's The Incredibles, and 14 years later, she finally reprised the character in Incredibles 2. But in-between those two movies, Hunter also lent her talents to the realm of live action comic book movies by playing Senator Finch in 2016's Batman v Superman: Dawn of Justice. Aside from both following costumed characters, Batman v Superman and the Incredibles movies don't share a lot in common, but Hunter has noted one similarity in her experiences working on Batman v Superman and Incredibles 2: she wasn't given an entire script for either movie, though for different reasons. Hunter explained:
With Batman v. Superman, I had part of a script, a fragment, but that was under lock and key for all different reasons. Incredibles 2 wasn't under lock and key, but that's part of the methodology of constructing an animated movie: It's made out of order in a way that a regular movie isn't.
With Batman v Superman: Dawn of Justice, I could see why why Holly Hunter didn't receive the whole script. That movie may have only been the second entry in the DC Extended Universe, but between starring two of the most famous superheroes of all time (and having Wonder Woman in a supporting role) and being the main building block for other DCEU movies to come, Warner Bros and DC undoubtedly wanted to make sure that as few spoilers leaked from the production as possible. By only giving some (or all) of its actors a partial script, that decreases the chances of key plot details inadvertently making their way to the public. Marvel took a similar approach with the actors in Avengers: Infinity War and Avengers 4. Plus, Hunter's role in Batman v Superman wasn't nearly as big as it was in Incredibles 2, so it wasn't quite as important to clue her in on the entire story, particularly (SPOILER alert for the few of you who still haven't seen Batman v Superman) in the latter half.
As for Incredibles 2, like Holly Hunter noted, putting together an animated movie is different than making a live action movie, so there wasn't so much a need to keep certain story details under wraps as working within this alternate process. Subsequently, Hunter also admitted during her interview with Vulture that she was surprised by "fully half" of the sequel, with even scenes that she'd read containing revelations when she finally watched the completed movie. At least we can be glad that at no point during Incredibles 2 is Elastigirl given a jar of Granny's Peach Tea.