She may be at the perilous age of 36-years-old -- for a leading actress at least -- but Cameron Diaz isn't worried about being typecast as, of all things, a mom.

"I didn’t think about it, in terms of what it meant to my career. I thought of what it meant to the story, and who this woman was and what her life experience was and what was happening in front of her," Diaz says. "I didn’t think, 'Oh, my God, if I play a mother, and a mother of teenagers, how is this going to affect my career?' It didn’t even phase me."

The comedienne takes the jump into motherhood in the new melodrama "My Sister's Keeper."  Directed by actor's favorite Nick Cassavetes, "Sister" finds a young girl (Abigail Breslin) trying to legally emancipate her body from her parents after its revealed she needs to donate her kidney to her cancer-striken sister ("Medium's" Sofia Vassilieva).  It's a tear-jerker of epic proportions and allows Diaz to show a dramatic side she rarely gets to indulge in.

Cassavetes tries to make the film as unconventional as possible by breaking up the story structure and revealing many secrets and character traits in flashbacks.  With Vassilieva shaving her head to play the sick sister (a requirement that caused Dakota Fanning to ditch the project), one scene finds Diaz's character joining her in a show of mother/daughter solidarity.  As Diaz jokes "don't believe the tabloids," she didn't need to shave her own head for the short scene, but she was incredibly impressed with Vasillieva's bravery in doing so. 

Diaz notes, "She was 15 when she did it. If anybody thinks back to when they were 15 years old, the last thing you want to do is shave your head and then your eyebrows. That’s when you’re getting a real sense of who you are. It’s so formidable. It was very brave for Sofia to do. It was amazing."

The "What Happens in Vegas" star was also impressed with her other big screen offspring, one-time Oscar nominee and "Little Miss Sunshine" star Breslin.

"What was amazing about working with Abby was that I realized you see her and you’re like, 'Oh, she’s just a little girl,' but she’s got so much power within her," Diaz says.  "I went up to her mother and said, 'Your daughter is a warrior.' She possesses something inside herself that is of the nature of a warrior, where she just knows how to push through. She can take all these things that are happening around her, that are these very adult, complicated, complex situations and ideas, and she’s able to somehow put something behind it with more strength than you see in most people."

Up next for Diaz is Richard Kelly's unconventional thriller "The Box" which Diaz describes as "Kubrick-esque." And, of course, her never-ending role of Princess Fiona in "Shrek Forever After."

"I’m just so honored to be a part of 'Shrek' still," Diaz proclaims.  "It’s a wonderful gift that gives to everyone, and I love being part of it."

"My Sister's Keeper" is now playing nationwide.