Three men wearing fake suicide bomb vests were shot dead by police after driving into pedestrians on London Bridge and stabbing people.
Seven people were killed and a further 48 were injured.
The police arrested 12 people in Barking, east London on Sunday during a dawn raid.
Amy Webster was in Borough Market, along with her boyfriend Ryan, when the attackers tried to make their way in.
“There were glasses being chucked around, bottles, and then people were throwing chairs,” she told BBC Radio Foyle.
“People at the back of the restaurant started screaming and running away from it.”
“We started to run away and it wasn’t until after a couple of minutes the manager managed to get the guys out of the restaurant and close the shutters.
Ms Webster explained: ‘We started to come back into the restaurant and someone was saying: ‘A girl’s been stabbed.’
“Basically, three men had come in with knives and stabbed a girl next to the door.”
The so-called Islamic State group has claimed responsibility for the attack.
“My partner saw one of the attackers briefly,” said Amy Webster. “He saw a man holding up a big knife that [he said] was about a foot-and-a-half long and waving it about.”
“We thought it was all over. I was getting our bags together and i was down next to the door and then we started hearing gun fire outside.
“We heard about four rounds of gun shots, in hindsight that was probably the police but we didn’t know they were there at that point.
“I found leaving the restaurant was almost the scariest part. We didn’t know what was on the other side of the door,” she added.
The 26-year-old, who survived a 7.8 magnitude earthquake in Nepal in 2015, said that when the police arrived, everyone was asked to “keep their hands above their head”.
“We walked past a couple of other bars that were also attacked, there was a lot of blood on the ground and there was people still in the bars that were injured and were being treated. It just seemed chaotic,” Ms Webster said.
“We feel incredibly lucky.
“There were so many people who weren’t as lucky as we were to walk away unharmed.”