Rebecca Bell, 30. of Locomotive Street, Boston admitted assaulting the officer when she appeared before magistrates in the town on Wednesday.
Paul Wood, prosecuting, said two officers went to her home on July 4 to arrest a man who was her friend, but she objected to their making the arrest, although he himself had submitted himself peacefully to arrest.
Mr Wood said that Ms Bell went out of the house, apparently to attack one of the officers, but when the other officer followed her to prevent any assault, she turned round and struck him twice in the face with her fists.
He said there was 'no justification or provocation' for the attack.
Ms Bell, who was not represented, told the magistrates that she hadn't been intending to hit him but was trying to get back into the house to 'stop my friend being arrested'.
The magistrates gave her a two year conditional discharge and ordered her to pay a total of £26 in court charges.