Chaynee Hodgetts, mitigating, said the row erupted after Allen found out boyfriend cheated on her with the other woman while she was pregnant with her daughter, who was now aged 15 months.
Hull Crown Court heard Allen, who has a baby daughter and a young son, has convictions for 11 previous offences.
The horror unfolded on April 5 at the Fiveways Hotel in Hull after Allen discovered her boyfriend's deceit while she'd been pregnant.
She stormed over to the victim, who had her back to Allen, and hit her on the side of the face - leaving her screaming out in pain.
Kirsty Allen flew into a rage after rumbling the affair that she grabbed a hammer and burst into a pub hell-bent on revenge.
