Caroline Salisbury, 28, from Suffolk, continued to groom a soldier’s son despite warnings to stay away from him.
She admitted having sex with him on four occasions and had been sentenced to a two-year suspended jail term.
The boy’s family argued the sentence was too lenient and three judges at the Court Martial Appeal Court agreed.
The original sentence was immediately replaced with imprisonment after the court heard she had sex with the boy on four occasions over three weeks in 2013.
She told the infatuated teenager not to tell anyone and, when the relationship came to light, claimed he had raped her and tried to delete messages they had exchanged by social media.
Salisbury had pleaded guilty in February to four charges of sexual activity with a child and was given the suspended sentence.
The boy’s family complained and the sentence was referred to the appeal court by Attorney General Jeremy Wright as being unduly lenient.
Sir Brian Leveson, sitting with Mr Justice Kenneth Parker and Mr Justice Stewart, said: “In our judgment, the very least sentence which could be passed is one of three years imprisonment.”
Mr Wright said later that Ms Salisbury “clearly took advantage of a teenager”.
“The original sentence failed to fully reflect the degree of planning and the serious breach of trust in these offences.
“The fact that Court Martial Appeal Court has imposed an immediate prison term on Caroline Salisbury sends out a strong message that teenagers have a right to be protected from sexual abuse.”
By- BBC NEWS Culled from: http://www.bbc.com/news/uk-england-suffolk-33004121