Naomi Jones, now 19, admitted killing her best friend Elysia Ashworth, 17, as a court heard she drove "unacceptably fast" while approaching a blind bend.
She was today jailed for six months, as a judge noted there may have been an "element of showing off to your friends in the car and those following''.
Jones, who wept as she gave evidence to the court, claimed she had been left "completely devastated" by the death of her friend, whom she had known since they were 13.
Miss Ashworth's family, who had written to the judge to express their feelings of injustice that their daughter's life had ended while Jones's would continue, were separated from the defendant's parents by a uniformed police officer.
The pair had regularly enjoyed sleepovers at each other's houses, with Jones going on holiday to Cyprus with Miss Ashworth's family three years ago, the court heard.
The families are said to have been torn apart when Jones lost control of her Vauxhall Corsa on the narrow, uneven road, which left rear seat passenger Miss Ashworth with multiple injuries.
Miss Ashworth died two days after the crash, which happened near Blackpool Airport on July 11 last year as the girls drove to visit her boyfriend.
Jones, who had passed her driving test four months earlier, said she failed to negotiate the left-hand bend in Division Lane after she hit two bumps in the derestricted road in quick succession.
An accident investigator later examined the scene and estimated the speed at point of impact with the tree at between 30mph and 35mph. It could not be determined what her approach speed was but it must have been greater than 35mph, the jury was told.
She admitted death by careless driving, but was cleared of the more serious charge of death by dangerous driving.
Sentencing her at Preston Crown Court, Judge Christopher Cornwall said that verdict should not be called into question but in his judgment it was not far short of dangerous driving.
Judge Cornwall told her: ''There seems to have been every conceivable reason that you should have reduced your speed on that road
''There is no doubt in my mind that the considerable jolt you experienced ought to have acted as a warning that your speed was unacceptably fast.
''There was no evidence of braking only a desperate attempt to steer around the corner which failed.''
He accepted she was not racing but pointed out ''there may however have been an element of showing off to your friends in the car and those following''.
He continued: "Your speed was wholly excessive and you now have to live with the terrible burden that you have brought the life of your friend to an end."
Jones, from Wesham, will spend her sentence in a young offenders' institute. She was also banned from driving for 12 months and ordered to take an extended re-test.
During the trial, Blackpool Sixth Form College student Jones said she was "completely devastated" at the loss of her best friend and had required reconstructive surgery for a broken left arm and right ankle.
She claimed she had to use a wheelchair for two months and still had pain in her ankle, had been diagnosed with post-traumatic stress disorder and suffered nightmares and flashbacks about the accident.
In a statement to police given several months after the crash, she said: "There has not been a day since the accident that I have not thought about the accident and Elly [Miss Ashworth].
"I have been left completely devastated by the consequences of this accident but I know whatever I am going through does not compare to the suffering felt by Elly's family and my thoughts are with them always."
Another girl in the car, Ellen Richardson, also suffered serious injuries in the collision but was recovering and was studying at university, the court heard.
Michael Shorrock QC, defending, said his client had to "live forever" with the knowledge she had killed her best friend.
He added her "supportive, loving family" would help Jones deal with the "terrible, terrible" consequences of her driving and that she had already been "severely punished".
Judge Cornwall said: "In circumstances such as these there is no direct relationship between the sentence of the court and on the other hand the inexpressable grief of Elysia's family... the value of Elysia's life is beyond all measurement and calculation."