Police with sniffer dogs were called in to search for a male suspect, who fled the scene, and St John Ambulance treated the victim.
Vicky did not require hospital treatment and went home early with "a bit of a headache".
Police took items for forensic testing.
The assault comes after months of "strange" activity in the empty space above the store. Previously they found blankets and pillows - but believed whoever was living there to be "harmless" and simply looking for shelter.
There were other signs too - empty toilet rolls, loo seats left up, clothing dumped at the back door and unusual noises overhead. They discovered whoever was bunking down had been coming in through the fire escape.
After Ms Booth walked in on a man sitting on the toilet, with the door open, early one morning, they called police, and secured the suspected entry point.
Recently, though, strange sounds surfaced again and they began taking precautions - pairing up for bathroom breaks, or using public rest rooms nearby to avoid going upstairs.
Plans to move premises were already in the pipeline and the relocation could not come soon enough for Donna.
"It's huge up there, empty rooms above the shops ... I felt a bit sorry for whoever was up there, I thought it's just a homeless guy, I didn't think for a minute he would be dangerous like that, she wasn't going up there to disturb him."
Donna said she and her staff were left shaken by the attack and decided to shut up shop for the rest of the day.
Cake Stuff will reopen as usual today, the final day before it relocates.
