Speaking from the witness box during her trial for assault this week, the 25-year-old singer described the incident at a charity gala last September.
Amy said that she'd been happy to pose with the well-wisher, but asked her to wait for a few minutes while she said goodbye to a friend.
"I didn’t know what she was going to do," said the chanteuse of the incident, which took place at the Berkeley Square summer ball, where she was dueting with her goddaughter, 13-year-old Dionne Bromfield.
"She lunged at me and put her arm around me. I think she was being overfriendly, but that was intimidating," she added." I'm not Mickey Mouse. I'm a human being."
Describing the push, Amy - flanked by her dad Mitch and four security guards as she arrived at court in a grey pinstripe suit - said: "It was more like an indication of 'leave me alone'…I meant to just get her away from me - I was scared of her.
"I am probably only five foot two or three... She's a big girl. I was scared," she continued.
Prosecuting, Lyall Thompson argued that his client Sherene politely asked the Back To Black star for a photo, but Amy responded by punching her in the eye using "unjustifiable violence".
If convicted of common assault, Amy, who recently returned from a controversial stay in St Lucia, could face up to six months in jail or a £5000 fine.