Becky Reid has been found guilty of murdering Wigan mum Lyndsey Vaux but her mother Gillian has been cleared of the same charge.
"Bullying" Reid, 32, regularly kicked, punched and stamped on mother-of-one Lyndsey Vaux, 30, leaving her "looking like the elephant man", Manchester Crown Court has heard.
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On Thursday a jury found her guilty of murder and grievous bodily harm to another previous partner, Samantha Newns, following a six-week trial.
Reid's mother, Gillian Reid, 57, was cleared of murder but found guilty of assault occasioning actual bodily harm to Ms Newns.
Both will be sentenced on Friday with Becky Reid facing a mandatory life sentence for murder.
Around a dozen members of Miss Vaux's family, including her daughter, aged 13, shouted "Yes" as the jury foreman delivered the guilty verdicts.
Outside court they hugged each other in tears and thanked police detectives who investigated the murder.
Judge Richard Mansell QC thanked jurors for sitting on a "very distressing case" and said he would speak to Miss Vaux's young daughter in private on Friday.
Earlier the court heard Miss Vaux died on May 22 last year having suffered 90 separate injuries following years of abuse by Reid.
Neighbours, shopkeepers and other witnesses told how Miss Vaux was often seen being dragged by her hair, punched, kicked and stamped on by Becky as she screamed abuse at her in the streets around their home in Platt Bridge, Wigan.
In the final months before her death Miss Vaux appeared downtrodden, malnourished, constantly bruised and going downhill rapidly.
One neighbour told jurors she "looked like she was dead already," and another said Miss Vaux looked like she had been in a car accident.
Inside the Reids' home jurors heard that on one occasion Becky kicked Miss Vaux hard in the face for putting salad on her burger.
Often Miss Vaux would be sent out limping in the streets in the rain begging and scrounging by Reid to get money for scratchcards, "smoke and cans" to feed her own alcohol and cannabis habits, and if she did not bring back enough money would be beaten.
Jurors heard police were called numerous times but Miss Vaux would make excuses for her injuries and refused to co-operate.
Experts concluded she died not from a single fatal injury but from the combined effects of multiple injuries over several months.
Miss Vaux had lots of friends in Stockport before she began a relationship with Reid in 2009 and moved to the Wigan area and lost contact with her daughter.
Becky Reid denied using any violence against Miss Vaux at all.
As police investigated her death they became aware of an earlier partner of Becky Reid, who was also beaten up by both mother and daughter.
Ms Newns met Reid in an online chat room for lesbians in 2004 and they began a relationship which became increasingly violent.
Miss Newns said she was assaulted around 50 times by Reid.
Prosecutor Paul Reid QC, told jurors: "It is the prosecution case that Samantha Newns was lucky in that she managed to extricate herself from her abusive and destructive relationship with Becky Reid before she suffered the same fate as Lyndsey Vaux. Lyndsey Vaux was not so lucky."
Both defendants will be sentenced on Friday morning.