A drug and drink fuelled teenager who set on three other girls with a rounders bat received 15 months' detention at Croydon Crown Court on Tuesday.
The incident on January 5 left one girl with a broken nose and another diabetic teenager running in fear.
Susan Gunton, 18, of Hunter Close, Wallington, admitted two charges of causing actual bodily harm and one of common assault.
The court heard how Gunton, fuelled with cocaine and whisky, set about in search of Kirsty Hill, 18, who knew her ex-boyfriend.
Prosecuting, Kate Ryle said: "She punched Miss Hill and hit her with a rounders bat, knocking her unconscious, the victim had five blows to the back of the head.
"Her friend, Shelley Bond, intervened and the defendant hit her with the bat on the back of the head and neck, making her giddy. "Because she is a diabetic, she was afraid of collapsing and she ran off."
Later, Kirsty's older sister Jemma, 20, heard what had happened and she and friends came up to Gunton.
"Insults and swearing were exchanged between them and Gunton punched Jemma in the face. It broke her nose."
The court heard that Gunton also used a haymaker punch, a type of move that uses the body's whole weight to throw the punch.
Defending, Rina-Marie Hill said Gunton had been having a difficult time following the break down of her four-year relationship. "There was some animosity between the parties," she added.
"She had some whisky and a small amount of cocaine and this had impaired her judgement.
"She took the rounders bat and watched for Kirsty.
"She accepts she hit Kirsty with the bat."
Judge William Barnett QC said the serious feature was that Gunton went out with a weapon, adding: "When people go out with weapons, all sorts of damage can occur."
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