Claire Marsh, 18, is believed to be one of the youngest of the few woman convicted of rape in the UK.
She was among a group of up to 12 youths who attacked a 37-year-old woman on a London canal towpath in July last year.
Marsh, from Margate, Kent, pinned down the victim, punched her and ripped off her top.
Her two co-accused, aged 15 and 18, were sentenced to five years in a young offenders' institution after admitting the rape.
Marsh had denied the attack but was found guilty by a jury last month.
Her sentence will also be served at a young offenders' institution.
Abortion
Marsh's lawyer, Iain Morley, revealed the teenager was 19 weeks pregnant.
She was due to undergo the final stages of an abortion on Wednesday.
Mr Morley said that Marsh went off the rails after she left home because of rows about her boyfriend.
She slept rough in a west London park, where she fell in with a gang of youths.
Mr Morley said publicity about Marsh's conviction had made her "notorious" among women prisoners, who had threatened her.
This had forced prison authorities to hold her away from other inmates.
Marsh decided on an abortion because she feared she would not be able to raise her child safely in a special wing of the unit because of her unpopularity, he said.
The jury at Blackfriars Crown Court last month had heard how a 15-year-old boy tore off the victim's trousers and raped her while others in the group shouted encouragement.
When the first youth had finished, Marvin Edwards, 18, also raped her.
Edwards, of Brentford, west London, and a 15-year-old admitted rape at the start of the trial.
Judge Timothy Pontius warned last month that "given this was a particularly vile and horrifying offence of sexual brutality" a custodial sentence was inevitable.
Thrown in canal
During her evidence, the victim, known only as Miss X for legal reasons, told the court she had decided to head home after a "lovely summer's evening" drinking but began chatting to a young couple on a bridge over the canal.
The pair offered to share a "spliff" with her before another dozen youngsters suddenly joined them, including three more girls.
The victim told the court how she was surrounded and robbed before being thrown into the canal.
She had no choice but clamber back on to the bank where her attackers waited.