Sienna Miller was ''terrified'' about making her new film.

The actress stars in 'American Woman' and features in every scene, the first time in her career she has done so, and she admits that left her worried.

In an interview with ITV's 'This Morning', she said: ''I really wanted it to fall apart. I have never been in charge of a story without the support of a man ... To be able to map something out in its entirety was something I loved. I'm really proud of it as I feel I couldn't have done anymore.''

Sienna plays a woman whose teenage daughter goes missing and her attempts to cope. When researching the film, she met people who had lost children, something that hit home given that she has a young daughter, Marlowe.

She added: ''I spoke to many people, it is not something you want to imagine but I wanted to get an understanding. I got to go home to my daughter, which made it even more poignant ... It was uplifting, in a way, seeing how these people had put their lives back together.''

The 37-year old actress believes that the film does not stick to a typical genre.

She explained: ''It's an oddity. It's a story about a woman growing up rather than a thriller. It's not about it's more about what happens to those left behind.''

Sienna stars alongside Christina Hendricks, who plays her sister, in the flick and director Jake Scott had a strange method to create a sisterly bond between the two.

Sienna shared: ''He told us to go and put make up on each other, as he thought sisters might have done. It was mortifying though, Christina thought it would push us further apart.''