Renee Joy Payne, of Launceston, has pleaded not guilty to wounding her boyfriend's sister in 2012 at her Prospect home.

In her opening, Crown prosecutor Virginia Jones said Ms Payne hit the woman in the face with a beer bottle.

Ms Jones said it occurred after the woman told the accused not to speak badly about her mother, who was asleep in the lounge room.

In his reply defence counsel Greg Richardson told the jury that self-defence was a "live issue".

The alleged victim told the court the group was having a good night as they danced to Michael Jackson with Ms Payne showing everyone the moonwalk.

However, Ms Payne began ranting that the woman should be pissed off because her mother didn't give a f--- about her, she said.

After telling Ms Payne to desist she felt a "bang" on her face.

"(I ) fell to the floor and there was a lot of blood everywhere," she said.

Mr Richardson grilled the woman over how much she'd drunk that night and if she'd been fighting with her husband.

The court heard she had a blood-alcohol reading of 0.224 when tested at hospital.

Mr Richardson suggested she was the aggressor that evening.

"Did you tell her you would use her face as a punching bag," he asked.

"No," she replied.

The woman denied telling Ms Payne she'd punched her brother's ex-girlfriend before or she had a tattoo for every person she'd "dropped and smashed".

However, she did admit being a boxer about six years before the incident.

Mr Richardson then produced messages by the woman saying she wanted to "smash" Ms Payne following the incident.

He suggested his client hit the woman after she was shadow boxing in Ms Payne's face.

The woman denied this.

The case continues in front of Justice Robert Pearce.