Toni Collette really wanted Drew Barrymore to be her best friend — in a movie, that is. And she got her wish: In Miss You Already, out November 6, the two play longtime pals. Milly (Collette) is undergoing cancer treatment when Jess (Barrymore) learns she is pregnant.Collette wrote to Barrymore "begging" her to be in the film. Why Barrymore? “She’s the ultimate girls' girl," Collette explains during a recent interview in New York, as her co-star sits beside her. "She’s so vocal about all things female. She’s strong and grounded and emanates an amazing warmth. And if you’re thinking about, oh, who would I like to play my best friend? It’s kind of a no-brainer.”Collette's powers of persuasion worked. "I picked up the family and moved over to London and I showed up and just said, 'I am here. I want to be with you, I want to support you, I want to be your backbone, I want to challenge you, push you when you need it,'" says Barrymore, who is an editor-at-large for Refinery29 . “I think we showed up with a lot of conviction to really have each others' backs. We just started laughing and had a blast from there on out.”Despite the trauma inherent in the film’s premise, Milly and Jess’ relationship is defined by the fun they have had together over the years. In one climatic moment, they flee an uncomfortable party in a taxi cab and head for the moors made famous by Wuthering Heights, a book they've adored since childhood. Barrymore and Collette just did a lot of "eating and drinking" for off-set bonding. "Which in itself can be wild," Collette adds.