There was no indication Swan had braked at any time.
At the time, Whanganui Fire Service senior station officer Bryce Coneybeer said the crash "must have been very spectacular".
Swan was taken to hospital and a blood sample was taken. It revealed she had methamphetamine and tramadol in her system.
She was also driving in breach of her restricted licence.
"In explanation the defendant stated she remembered turning on to Bell Street and feeling an impact," the summary of facts said.
Swan couldn't remember how she crashed into the shed.
She pleaded guilty in the Whanganui District Court to careless driving and driving under the influence of drugs.
On Tuesday, Judge Patrick Treston fined her $500, $130 court costs, $652.63 for the blood analysis, and disqualified her from driving for six months.