The former X Factor judge, 27, was banned from driving for 15 months after admitting being over the limit in the incident outside Southgate Tube station in north London on 10 September last year.
Contostavlos said she was “sleep-walking” or “sleep-driving” in an interview at the police station afterwards, prosecutor Tarika Jayaratne told Highbury Corner Magistrates’ Court.
The singer, who arrived wearing sunglasses, has plans to launch an acting career with hopes to “break through” in the US, the court heard.
Mitigating lawyer Kirsty Brimelow QC said Contostavlos is “a very talented young woman” and is signed up by an agent in Hollywood, adding: “She has placed everything on hold because of this.”
Ms Brimelow said the conviction will cause the star “difficulties” working in America.
Contostavlos broke down in tears when she was asked to state her Enfield address.
When it came to giving her postcode, the star wept and said “sorry” before sitting down.
Ms Brimelow tried to prevent Contostavlos having to give her address in open court.
She said the singer receives “a lot of unwanted attention because she is famous” and spoke of the “real risk” involved in her address being known, adding that she has had to move in the past.
But District Judge Gill Allison dismissed the application.
Contostavlos pleaded guilty to driving with 54 microgrammes of alcohol in 100 millilitres of breath – the legal limit is 35 microgrammes.
The former N-Dubz star was ordered to pay a total of £1,185 and disqualified from driving. A charge of dangerous driving was dropped by prosecutors.
The court heard that Contostavlos had consumed two glasses of wine before the incident involving her Ferrari Spider, which she has since sold.
Ms Jayaratne said the star drove “on the wrong side of the road” and hit a vehicle which was carrying two people.
Contostavlos, who was held by police for 22 hours, is remorseful about what happened, Ms Brimelow said.
The QC described the incident as a “minor collision” and told the court that the people in the other car were able to drive home after it happened.
“She immediately co-operated with police,” the lawyer said of Contostavlos, adding: “She immediately told the police that she had drunk alcohol.”