The fact that YM looks like Audrey Hepburn has been brought up alot of times before. She's even hailed as the Audrey Hepburn of China by the mainland press and her fans. I think that their eyes, nose and most importantly, their face shape is very similar, they both have very sharp jaw lines.
YM's also said to resemble Shui Ling, especially her nose and eyes. I think she looks alot like Shui Ling in this pic.