There’s nothing wrong with this sentence, except for the fact that no pun was intended.
The student was writing about the case of a young woman who had a roll in the hay with her boyfriend and then panicked that she might have become pregnant. Looking for a way to exculpate herself and shield her boyfriend from parental wrath, she fabricated a rape charge, chose a “rapist” at random from a mug book, and stuck vehemently to her accusation even after her body gave her an all-clear on the pregnancy scare. Convicted solely on the strength of her testimony and the weakness of his alibi, the hapless man did eight years in prison before Jane decided to recant, and then she couldn’t get the conviction overturned. This case was in all the newspapers, and produced some interesting student essays (and a few pretty scary ones, actually).
So my student is right: Jane thought she was pregnant, but she was wrong.
This was not a student given to puns, or even to moments of writerly wit, so she must have been visited at the typewriter not by her muse, but by the impish ghost of Sigmund Freud, who prompted a word choice that was unimpeachable for accuracy but hilarious for the pun.
Certain topics do this to people more easily than others. Another student writing on the same case said “By having sex with her boyfriend she opened herself up to the possibility that she might get pregnant.”
As for the “rapist,” “Once he is convicted, he is found guilty.” Although without unintentional puns, another student’s strange but accurate report of Jane’s failure to undo her lie is still worth remembering: “She unsuccessfully persuaded the judge to set him free.”
Curious about how it all came out? Jane went to the newspapers and to the governor, and finally the imprisoned man was granted a pardon. Nevertheless, his life would never return to normal: “The bottom line is when people go to jail they come out a changed man.”