The singer loves everything the Louis Vuitton creative director makes, not just his clothes.
She said: ''One of my favourite designers is Marc Jacobs. I'm always a huge fan of what he makes whether it's a mouse ballet flat or an iPhone cover with bunny ears.''
The star - who has four-year-old son Bronx with her ex-husband, Fall Out Boy bassist Pete Wentz - is especially a fan of the latter two's effortlessly style because she knows how hard it is to look chic as working mother.
She told Life & Style magazine: ''I love Gwyneth and Gwen's style. They are cool moms with an amazing ability to walk out of their houses looking perfectly chic and styled.
''If I could raid anyone's closet though it would be Diane Kruger. She always has the most amazing designer pieces.''
Ashlee caused a stir when she debuted her super slender figure at New York Fashion week earlier this year, but has spoken openly in the past about not being concerned with her weight.
She said: ''I wanna look good [for me]. I wanna feel good ...There's gonna be a time when I'm way curvier, and that'll be sexy too.
''What defines sexy is not someone's weight. Personally, I like curves.''