She is voiced by Christina Applegate, who also voiced Catherine from Cats & Dogs: The Revenge of Kitty Galore.
Her personality is toned down. She is a lot friendlier and polite, making it easier for others to approach her. She is nicer and has better control over her temper then Alvin does, though it is still a bit shorter then most.
Alvin and the Chipmunks: The Squeakuel
Brittany and her sisters met Ian Hawke and was hoping that she and her sisters would meet the Chipmunks but Ian told them that they already left him. He also told them that they made him very upset because Alvin literally spat on him and he didn't want to mention the other two making the Chipettes believe that the Chipmunks are mean just to take revenge against the Chipmunks and became very excited to use the Chipettes as his minions. When she and her sisters meet the Chipmunks at school she tells her sisters that Ian said they can't trust them. Later she and her sisters sing a song on stage to help Ian convince Dr Reuben to let both the Chipmunks and Chipettes sing at the school concert, but she initially refuses but she finally agrees. At lunchtime Brittany encounters Alvin who tells her that she shouldn't trust Ian because he's cruel but she doesn't listen. After she and her sisters sing at the school concert she discovers that Alvin didn't come which made her and the Chipmunks very upset and tells Alvin and Ian was right that he doesn't care about anyone but himself and she never wanted to win this way. When she and her sisters are approached by Ian to inform them about the over singing concert at the Staples Center, she and her sisters are initially excited but they realize that this means they'll missed the school contest and when Ian tells them that will be singing however he wants them to which means mainly having Brittany so they refuse unless they all sing together. Then Ian threatens them by grabbing their tales and holding them upside down and hurting them making Brittany realize that Alvin was right about Ian. She gives Alvin a phone call to let him know that Ian locked her and her sisters up in a cage and Alvin goes to save them. After Alvin saves the Chipettes from Ian they go to the school concert to perform and they all became friends and are now under the care of Dave Seville.
Alvin and the Chipmunks: Chipwrecked
Brittany and her sisters and the Chipmunks go on for a cruise to the International Music Awards to perform, but when they borrow a kite they accidentally got shipwrecked and go to an island. At the island they meet a strange woman named Zoe who takes them under her wing. When Alvin and Brittany decide to build a shelter Alvin becomes upset about Dave not looking for them because he annoys Dave so much for a few years but Brittany kindly and warmly comforts Alvin and tells him that she's sure Dave will come. Later when Brittany and Alvin discover a active volcano Alvin tells everyone that they need to get off the island by building a ramp but Zoe had other plans by finding the treasure behind the waterfall and plots to use them to get the treasure for her. When Dave arrives with Ian Hawke the Chipmunks and Chipettes are all excited to see Dave again all except Alvin who was worried that Dave wouldn't find them but Dave tells Alvin that he'd come no matter making Alvin very happy and gives him a hug. After making the raft with help of everyone they discover that Simon and Jeanette are missing while they were bringing some food for the others Simon gets hit on the head by one of Zoe's ball friends and the other one chases Jeanette and captures her. When the others look for Simon and Jeanette they discover Simon lying on the ground but Jeanette was gone then Brittany discovers that Zoe took her to the waterfall so they all go to find her when they arrive at the log bridge Dave tells Ian to take everyone back to the ramp while he and Alvin go to save Jeanette. When they rescue Jeanette Zoe returns and takes Jeanette by force using the rope that she put on Jeanette but Alvin cuts the rope then they all run back to the raft, but Dave accidentally and nearly falls of the log. Then when Zoe is just about to make Dave fall down Ian arrives to convince Zoe to stop and help Dave up then they all run back to the ramp and escape the vanishing island. Later while sailing on the ramp Dave discovers a helicopter and they all call out to the helicopter and they witness Dave and the others on the ramp and give them all a lift to the international music awards where they all perform with Dave and Ian watching them as they're all happy.
Alvin and the Chipmunks: The Road Chip
It's Dave's birthday and the Chipmunks and Chipettes throw a giant house party for him and they all start dancing around and having fun but when Dave arrives he becomes really disappointed so the Chipettes head out to the judge american idols. When the Chipmunks accidentally provoke Dave for stealing the engagement ring from Barry, Alvin decides to make Dave happy by singing a song and goes to the Chipettes for help. At the concert the Chipmunks and Chipettes perform for Dave making him very proud of them all. After Alvin thanks the Chipettes for helping them perform for Dave and Brittany comes up to Alvin and says "you're welcome" then they head back to the judge "American Idol" for auditions.