The attack on Masoomeh Jafari began when a group of five of the girls aged between 11 and 14 began abusing her in her shop.
The 26-year-old was called a a "f****** Muslim" because she confronted them about stealing at around 3pm on Sunday.
The girls were joined by a bigger gang which began to attack the shop worker.
Ms Jafari said: "They came in here shouting and stealing things and I told them to stop.
"A group started swearing at me, saying things about my religion and the clothes I wear. Then they grabbed my head scarf twice.
"I was very frightened."
Patricia Rose, 69, was passing the store in Sutton, London when it happened.
She said: "They were saying 'f*** this' and 'f*** that' and they were trying to get back into the shop after they had tried to steal things.
"I then went into Poundland and saw the lady. She is a delightful person and her head was down.
"She told me that the children had pulled at her hijab and had sworn at her.
"It's so, so wrong what they did."
The pensioner said police officers attended the shop but the group had left and there was no CCTV footage to help identify those involved.
Ms Jafari, who has worked at the Poundland for six years, added: "This has happened before. Sometimes they come in after school, sometimes on the weekends, we catch some of the children stealing from the shop and they are rude to us.
"I was really upset after it happened.
"I told my parents about it and they said that I should think about finding work somewhere else.
"But I have been here for so many years and this was not a problem until recently."
t was thought that some of the teenagers could have attended near-by Greenshaw High School but staff said they had not received a complaint about its pupils but would investigate if it did.
A Poundland spokesman also said they will look into the matter.
A spokesman from Sutton Police said it had no record of the abuse.
The spokesperson said: "We would encourage anyone who has been a victim of hate crime to report it and we will investigate it robustly.
Hate crime is an under-reported crime and should be reported when it occurs."
