The woman, who was 17 at the time, was sentenced in the Supreme Court in Launceston on Tuesday after pleading guilty to being an accessory after the fact in relation to the aggravated armed robbery in January last year.

The court heard she was present when the men devised the plan to lure a man to a unit in Waverley to rob him of cash and drugs, but did not participate in the planning.

When the man arrived at the address, she hid in the bathroom where she could hear the sound of the blows and the victim's screams, seeing part of the attack through a crack in the door.

The four men punched his head, face and body repeatedly, bashed him with a chair leg and tied electrical tape around his head and neck. The victim was then loaded into his ute, but fell from the tray and was left on the side of the road while his ute was dumped in a nearby lake.

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He was placed in an induced coma for five weeks.

After the attack, the girl used hot water, bleach, sponges and towels to clean up the substantial bloodstains on the walls and floor of the kitchen and living room, before placing the items in a plastic bag and disposing of them at another address. She also accepted some of the stolen cash.

She was arrested several days later, along with all co-accused, but denied knowledge of the attack during an interview with police.

When police found contrary evidence on her phone, she admitted to the crime but lied about not knowing two of the men.

Justice Robert Pearce said given the girl's age at the time, it would have been difficult for her to prevent the men from carrying out the attack.

He condemned her actions after the incident, however.

She was convicted and given a five-month jail sentence, suspended for 12 months, and placed on a 12-month community corrections order.