Renee Joy Payne, of Launceston, has pleaded not guilty to wounding her boyfriend's sister at a family gathering in October 2012.

Ms Payne does not deny smashing a stubby of beer on the woman's face at her Prospect home.

However, she claims the alleged victim, a former boxer, was the aggressor.

Ms Payne said she had a heated argument with the woman on the night.

"(She said) she was going to fold me up and put me in her pocket," Ms Payne told the jury in Launceston's Supreme Court yesterday.

"How did you perceive it," defence counsel Greg Richardson said.

"I thought it sounded pretty threatening."

Ms Payne said the woman threatened her.

"She went like that (shadow boxed) in front of my face," Ms Payne said.

"Straight away I just punched back."

Ms Payne said she was not conscious she was holding a beer bottle at the time.

Under cross examination Crown prosecutor Virginia Jones asked Ms Payne why she failed to tell police about the woman's threatening behaviour.

"I didn't understand what self- defence was," Ms Payne said.

"We just assumed it would be forgotten about."

Ms Jones said the accused was reconstructing the event "because you are trying to make up a defence".

Ms Payne denied this.

In closing Ms Jones said this was not a case of self-defence.

In his closing argument Mr Richardson said prosecution witnesses had colluded in giving evidence.

He said his client's punch "was an immediate reaction to an act of aggression" by the complainant.

The jury will consider its verdict tomorrow.