Michaela Jade Borman, 33, of Kyme Road, Boston admitted assaulting a police officer by beating when she appeared at the town's magistrates court.
Prosecuting, Marie Stace said officers were called to an incident in Kyme Road at 7.05pm on February 15 where they arrested a man who was drunk and behaving in a disorderly manner.
She said Ms Borman then arrived on the scene and got in between the arresting officer and his prisoner and tried to separate them.
She said the officer pushed her away and she fell over but she then got back up and grabbed the officer by his coat and slapped him.
Ms Stace said the officer handed his prisoner over to another officer and grabbed Ms Borman and the two fell over and she was arrested.
Ms Stace said Ms Borman later apologised to the officer and said she had not realised he was a police officer.
She said neither of them was injured.
Ms Borman told the magistrates she had no memory of the event and apologised for what had happened.
Fining her £50, the magistrates told her: “This is what happens when you get drunk and you can't remember what you do.”
She was also ordered to pay £119 in court costs and charges.