Police are hunting her attacker, who was described as an Asian man with a "very distinctive" pockmarked face.
It took place on Friday at 7pm in the car park of the John Lewis in Cheadle, near Stockport, Manchester. The woman is in her 20s.
Police described her attacker as of medium build, around 40 years old, with black hair and thick black ‘monobrow’ eyebrows.
Detective Inspector Richard Ennis said: “This young lady has suffered a deeply traumatic ordeal and we have a team of detectives who are working on this case to try and identify the man that did this to her.
“We believe that the area close to where the victim was parked in her car is used as a cut-through between Wilmslow-Handforth by-pass and the junction of Wilmslow Road and Etchells Road and we are appealing for anyone that may have seen a man fitting this description hanging around this area, to please get in touch.
“The description of this attacker is very distinctive, with deep pock-type scars on his face and I am hoping that this may jog someone’s memory to call us, so we can find the person responsible and take him off our streets.”
Anyone with any information is asked to contact police at Stockport on 0161 856 9770 or contact the independent charity Crimestoppers, anonymously, on 0800 555 111.