When she broke the news to him, the girl's father - in typical patriarchal fashion - accused her of being in on what was happening.
"Find ways of taking care of her," he scoffed at her, Naserian alleges .
Hence, when her emotions boil over talking about Sian, one can only imagine the psychological anguish she is going through. However, the thought process that leads to her emotional outpour may not be quite what you might think.
"In my culture, when a girl becomes pregnant while still in her parent's house, she is married off to the boy (man) responsible," Naserian says.
Under normal circumstances, that was the fate, unfortunately, that awaited Sian. Her younger and immediate sister got married in 2020 under similar circumstances.
However, Sian has a disability - she can neither hear nor speak. Because of this, she is not considered 'marriageable.'
"Because of her condition, I wanted her to study and become an independent woman: so that she can be able to take care of herself," Naserian says.
Even so, marrying her off to the man who impregnated her would not have been possible because: "Which man wants a wife who cannot talk or hear?"
In addition, Sian - who only communicates by writing down answers to questions - could not effectively identify the man responsible for her pregnancy.
"We have tried to get a name from her but so far we don't have much to lead us anywhere," she says.
We wrote the question, 'Who is the father of your child?' to Sian. She scribbled a name. "We don't know anyone with that name," says Naserian.
Sian could not comprehend follow-up questions that would have identified the man's locality. To date, the man remains a mythical figure.
For Dorcus Parit, a girls' rights activist, it is more worrisome that Sian could have been abused and neither the girl nor the family realised it.
"She can't talk or fully express herself. How can we be sure that she consented to the sex? Chances are very high that someone took advantage of her."
Stay informed. Subscribe to our newsletter
Parit is the founder of Hope Beyond Foundation (HBF), a community-based organisation operating in Kimana, Oloitoktok - where we met Sian and her mother.
"We rescue girls like Sian: girls who need to escape early or forced marriage, female genital mutilation, and other forms of abuse," she says.
Sian is now in Form 1 at a special school located in Murang'a County . She wants to be 'someone who types on a computer, takes notes, and receives phone calls,' as she motioned.
Naserian is convinced that Sian needs a good education for her future prospects. She has taken over the custody of Sian's six-month-old son to allow Sian to go back to school.
To protect her daughter from further unplanned pregnancies, the mother has resorted to placing Sian on long-term contraception: an implant.
"My daughter needs someone to accompany her round the clock for her own protection: not just against malicious men but also from being hit by a car or motorbike," Naserian saus.
"We are poor. I don't have the ability to hire someone to do that for us. I sell beadwork to tourists and I don't make much. The only thing I can think of is placing her on birth control.
"I would like her to finish school. Unlike her sisters, I am not sure she will find a suitor. I feel being educated can land her a job and assure her independence," she says.
The current challenge the distraught mother is dealing with is the inability to raise the approximately Sh20,000 tuition fees per term for Sian's education.
Legally, Sian could make the decision to take up family planning by herself. Her mother has however assumed the role of 'caring' for her.
Naserian's contraceptive decision for Sian is not uncommon in Oloitoktok. We spoke to two other parents who have put their daughters on family planning following a pregnancy.
"Teenage pregnancy is very high in Oloitoktok. Parents (mothers) have to take these drastic measures to protect their girls," says Nenkiposho Langeu, a community worker for HBF.
Martin Onyango, an advocate of the High Court, says a parent cannot decide for an 18-year-old whether to be on contraceptive or not.
"If the daughter has disability, they should be supported to make that decision for themselves. In Sian's case, she is mentally capable. She can also communicate - albeit in ways the mother may not be able to communicate back . Even so, she should not be subjected to forced treatment," says Onyango.
Dr Nelly Bosire, an obstetrician and gynaecologist, says it is important that every woman or girl in need of contraception, be tested and advised accordingly.
"The tests are recommended to rule out risks to health and wellbeing of the woman," she says. "Part of post-partum medical care includes being informed and counselled about taking up family planning."
Shalom Munyiri, a family life coach, says parents should proactively empower their children to have an age-appropriate understanding of sex and sexuality, "so that they would know how to respond when confronted by a situation that may lead them to sex."
Shalom takes note that while Naserian has taken steps to protect her daughter against pregnancy, there are still sexually transmitted diseases to contend with.
All this advice might not quite make sense to women like Naserian whose lives are uniquely trapped in an echo chamber of traditions and patriarchy.
Right now, she says, her focus is in making sure Sian gets the education she needs. With 'pregnancy scare' taken care of, Naserian says, her only battle is with poverty: finding fees to make sure Sian completes school.