Caroline Westlake said she wanted to “rebuild her life” after High Court judges quashed her conviction.
She was previously found guilty of “recklessly but not intentionally” causing a wound which needed three stitches on the cheek of colleague Kate Sanders during the argument at a London Zoo party.
Westminster magistrates found the 30-year-old guilty of assault by beating last September after hearing that the women had fallen out over keeper Adam Davies, who dated Ms Sanders for five years before starting a relationship with Ms Westlake.
But Lord Justice Laws and Mr Justice Nicol ruled that the magistrates applied the wrong legal test for recklessness and quashed the assault conviction.
Magistrates heard Ms Westlake was at the staff Christmas party in 2014 when she heard Ms Sanders ask friends, “Have you seen the state of her?”.
Later the women argued and Ms Sanders said as she tried to leave Ms Westlake smashed the glass into her cheek, leaving her face covered in blood.
Ms Westlake accepted the injury came from her glass but denied causing it deliberately or recklessly.
The magistrates ruled that Ms Westlake was guilty because she had been reckless and “failed to see the risk of injury” of holding the glass close to Miss Sanders.
But Lord Justice Laws said the correct test was “whether the defendant foresaw the risk of harm but went on to take it”.
He ruled there should not be a retrial because the magistrates had concluded that Ms Westlake, who was dismissed from the zoo after the incident, “did not foresee a risk of injury”.
Later her legal representative said: “Ms Westlake’s life has been destroyed by something that was no more than an unfortunate accident.
“Justice has now been served and she would appreciate the opportunity to put this matter behind her.”