Luckily that oversight is being rectified in the form of a new clip that has been released, which appears to also be the character's introduction in the film. Check out when Woody and Forky meet Gabby Gabby in the clip below.
A piece of this scene can be found in the trailer for Toy Story 4, but this clip extends that considerably. We see Woody and Forky inside the antique store where Bo Peep's lamp has been discovered. While looking for Bo, Gabby Gabby comes across the pair and offers to help them, since she knows Bo Peep.
Of course, one thing we do know from the trailers is that Gabby Gabby is the villain of Toy Story 4, so, while Woody and Forky don't know it at this moment, they are absolutely in trouble right now. As if the utterly creepy ventriloquist dummies weren't enough evidence for that.
This clip also gives a us a bit of understanding in Gabby Gabby's potential motive. We see her notice Woody's pull string in a way that makes it clear it is important. One thing we know about the character is that her own voice box is broken, which is part of the reason she's found in an antique store and not in a child's home. It's not hard to put this information together and figure out what Gabby Gabby's goal in Toy Story 4 will be.
Christina Hendricks voice is perfect as Gabby Gabby. She sounds absolutely adorable and sweet, which fits because that's the way the doll is designed to look, but we know Hendricks can be tough as well and that's going to come through when we see her drop her facade.
While Gabby Gabby might be our film's villain, it's unclear just how much of an obstacle she'll actually be. While the Toy Story films have had villains before, like Lotso and Stinky Pete, the previous films haven't been so much about overcoming them as they have been about much broader themes. The villains are usually more personifications (toyifications?) of those themes than they are simply bad guys to be defeated.
I would guess that will be largely the case with Gabby Gabby as well. Toy Story 4 appears to be about Woody coming to terms with his own existence after Andy. A lot has changed for him, and then he meets Bo Peep again, for whom even more has changed. He will see a potential future that he never considered before. Bo Peep and Gabby gabby are both "lost toys" something Woody sees as a terrible fate, but perhaps it's not quite what he thinks it is.
Toy Story 4 hits theaters June 21