McGonagall finds a Animagus Harry as a Red Tailed Hawk going by Tobias in an America town.

With a flick of her wrist he’s human again but he immediately asks her “Do you have a Worm in your head?!” Grabbing her shoulders.

McGonagall shakes her head, casting a spell showing a display of her brain then testing it on a Controler revealing a Worm in the skull.

Harry immediately introduced her to the Animorphs and tells them she can reverse permanent morphing and she can scan brains.

McGonagall turns into a cat when the rest of them turn into animals themselves and then is shown the Cube and learns these are muggle children who have super powers who are fighting an alien invasion.

McGonagall becomes the only adult that can be trusted by them against the threat and she brings them bottles of Animagus reveal potions that seem to cure permanent morphs and it turns out mixing Animagus training with The Cube grants Speed Morphing.