Vanya Louise Monet (45) attacked the man on Don Street on 2 February.
A trial in the Magistrate’s Court heard that Monet had banged the man’s head against a window pane and had kicked him repeatedly as he fell to the ground.
Monet denied doing so. She claimed that a noise that sounded as if she was kicking him was in fact an echo caused when she stamped her foot.
But Magistrate Bridget Shaw said: “It is not plausible.
“I am sure you committed a grave and criminal assault and I find you guilty.”
Monet will be sentenced on 8 September.