Minnie-Mo Hunt, 25, and her niece Daisy Hunt, 23, attacked Rebecca Grant on Southsea Common after she asked them to return a laughing gas cracker.
Portsmouth Crown Court heard the pair had joined 20-year-old Ms Grant’s group uninvited while they were sitting near the Queen’s Hotel on June 17 before taking the device used to open canisters.
Ms Grant was stamped on and kicked after standing up to the Hunts, who thought the group would be ‘too frightened’ to get the device back.
Aggressor Minnie-Mo Hunt had told Ms Grant: ‘Keep flashing your eyelashes on your pretty face and watch what you say or I will knock you out.’
Their ensuing attack was partly caught on video and went viral social media, having been seen more than a million times.
Jailing Daisy Hunt for three years, Recorder Gordon Bebb QC said: ‘Both of you by then were really acting as a pair of bullies.
‘You were intimidating and you thought that the group would be too frightened to do anything about it and that was partly true.
‘But the only person who wasn’t, was Rebecca Grant.
‘I’m prepared to accept that she went to try to get that item, the cracker, back, and I have no doubt that her trying to do that acted as a trigger for both of you to teach her a lesson.
‘Between the two of you, you got her to the ground and when on the ground, you Daisy Hunt, stamped on her head twice and you Minnie-Mo Hunt, deliberately kicked her in the face.
‘As a result of the stamping Rebecca Grant was knocked unconscious, and had to be taken to hospital.’
Ms Grant suffered no serious injury but was left with bruising, and remembered little between being knocked unconscious and waking in hospital.
Recorder Bebb said he ruled out the Hunts acting in self-defence.
Daisy Hunt of Berkshire Close, Landport, has previous convictions for assault in 2012 and 2013, and causing actual bodily harm.
She previously admitted attempting GBH.
Minnie-Mo Hunt, of High Street, Cosham, admitted causing actual bodily harm.
She was handed an 18-month jail term suspended for two years with 20 days’ rehabilitation activities.
As reported, she was cleared of attempting GBH at a trial in November.
Robert Bryan, for Daisy Hunt, said she was remorseful and tearful when interviewed by police after she handed herself in.
Mr Bryan said a report found she was ‘intrinsically not a bad person’ and had turned her life around at 19 having started abusing alcohol and drugs ‘at primary school age’.
Prosecutor Oliver Wellings said Minnie-Mo Hunt was the ‘aggressor’ who started the violence.
Viral footage of the attack shocked the Portsmouth community returning to life with fewer restrictions after the first Covid lockdown.