Hilary Duff and her sister Haylie co-starred in the film Material Girls (2006). Hailey is a singer/songwriter besides starring on the series 7th Heaven (2005-2006), and in such films as Napoleon Dynamite (2004) and thriller telefilm Deep Cove (2009). She's in the film Addams Family Reuinion (1998) which features a were-chihuahua amidst the characters.
Her young sister Hilary is the one most associated with chihuahuas, while Haylie's best known dog is her pomeranian Bentley, though strictly speaking Haylie co-owns Bentley with her mother.
But Hailey is also co-owner with her sister of Coco Chanel, whose love and care was entrusted over to them by Coco's former owner, their late grandmother. I could be wrong but I'm pretty sure Hilary has a completely different chihuahua which she had already named Coco before their grandmother's death, and that one's pale-fawn. It must confuse the two Cocos a bit when they all get together.
In the two photos above, Haylie is holding Bentley and Coco Chanel. Below Haylie and Hilary sit together at a dog charity, with a little chihuahua available for adoption. The benefit for Much Love Animal Rescue was held at Hugh Heffner's Playboy Mansion.