The 'Girls' star is a huge fan of the actress-turned designer - who boasts her own festival-themed clothing line for Topshop - and loves attending high profile events because she can rub shoulders with her favourite fashion stars.
Allison told LOOK magazine: ''I'm very interested in fashion and I love the fantastic outfits I've been getting a chance to wear to different events.
''I get to meet a lot of incredible designers and some of my idols - like Kate Bosworth. She's beautiful and has an amazing sense of style, and she also has her own fashion line now...
''I was very excited to meet her. And her eyes are, without question, the most beguiling and gorgeous eyes I've ever seen. I monitored my staring very closely, so as to not freak her out!''
The 26-year-old star also said her alter-ego Marnie in the hit HBO show couldn't be further from her real-life personality.
She explained: ''I'm very different, but I'm her biggest supporter. Marnie is still in the process of figuring out her life, whereas I've had the advantage of pretty much knowing what I wanted to do with my life - to be an actress - since I was five years old.''
There's already an Oscars buzz surrounding this movie.