She had failed in two subjects.
Ms Khushboo was one of the three students who committed suicide on Tuesday in Delhi alone, after the Class X board examination results were declared -- the government had brought back board exam for Class X in 2018 after a gap of eight years.
The board exam was scrapped in 2009 to reduce pressure on students.
"If children are taking lives in the name of papers (exams), then there should be not exams," Khushboo's father Daya Ram, 40, told IANS outside a mortuary of a city hospital, where he was waiting to receive her body after post-mortem.
"We worked very hard under the sun to bring her up, but she did not think about us," Mr Ram remarked stoically.
Mr Ram along with his wife Ms Soniya, 38, irons clothes near a park in west Delhi for a living.
In the narrow street outside Ms Khushboo's house in Dabri in west Delhi, her mother and aunt Ms Pooja, 24, who lives with them, were inconsolable.
Sitting on a cloth spread on the street, waiting for the body to arrive, Ms Pooja said between her loud cries: "She loved me so much that the mad girl hung herself by using my dupatta."
"I won't allow her to go, I will beat her for sure. For sure," she cried out as family members tried to console her in vain.
"Why did she do this?," she cried in a muffled voice, as a relative pulled her into a close hug.
While Ms Khushboo killed herself after failing in two subjects, the other two students took their lives after scoring low marks.
"After that she was lying on the bed and was sad about the result," her sister Ms Komal, 15, told IANS.
Around 4 p.m., Ms Pooja telephoned Ms Ram and told him about the results. "I told her that it is fine and not a problem," Mr Ram said.
After that Ms Pooja and Ms Komal went out for tuitions, but Ms Khushboo stayed back.
"'I will come in five minutes', she said and this was the last she spoke to us," Ms Komal said outside the house.
When Ms Komal came back around 7.15 p.m., she found the door to their first-floor house locked from inside.
She climbed into the house from the terrace of an adjoining house, as both of them shared a common wall.
"I found her hanging from the fan with a dupatta. Her left wrist was slit and there was blood all over the floor," Ms Komal told IANS.
Ms Khushboo wanted to be a doctor.
Family members said that they never felt that the girl was under any pressure. "Even when I left for work with my wife in the morning, she was laughing and playing," Mr Ram said.
According to a family member, a suicide note left behind by Ms Khusbhoo written on a paper with red ink in Hindi read: "I am leaving you people and going. I could not give you happiness. You people should stay happy."