Cheryl, 20, is on trial at Surrey's Kingston Crown Court for something called "racially aggravated assault", plus another charge of hurting Sophie.
Cheryl denies the charges.
Bryony said Cheryl has taken some lollipops from a display in the nightclub toilet where Sophie was working.
"The toilet attendant was saying 'I want payment for the lollipops' and Cheryl was saying 'I do not have to pay'," Bryony told the court.
"When the toilet attendant leaned forward to take away the lollies from Cheryl, Cheryl punched her," she claimed.
The trial is expected to last up to five days.
If Cheryl is found guilty by the court jury, she could go to prison.