Her father believes that she overslept on the bus and missed her stop, alighted and had to cross the road to the opposite side to catch the bus back.
While doing so, Lynette Chan, 17, was hit by a lorry and was flung several metres.
Mr Alvin Chan believes his daughter was on her way to collect her student testimonial document from her alma mater Tanglin Secondary School on Monday afternoon when the incident occurred.
It happened 2km to 3km away from the school.
The Singapore Civil Defence Force (SCDF) said it was alerted to an incident at 35 Teban Gardens Road at 2.39pm on Monday.
The girl was taken unconscious to Ng Teng Fong General Hospital, the police said.
The New Paper understands that she suffered traumatic arrest, which means she had some form of trauma that led to a cardiac arrest, before SCDF officers arrived.
The family is appealing for witnesses to come forward and investigations are ongoing.
The first-year accountancy Institute of Technical Education (ITE) College West student is survived by her father, her grandmother, two brothers, aged 13 and 14, and a 16-year-old sister.
Mr Chan, who is a single parent, told TNP that his daughter wanted to use the testimonial for a school project next week.
While she did not specify when she wanted to go to the school, she spoke about it to her siblings, her ITE schoolmates and her grandmother.
Mr Chan, 50, who works in logistics, said he was at work when he received a call saying Lynette was in a critical condition and arrived at the hospital with her siblings after 4pm.
He said she was found barely alive at the accident site and was pronounced dead at the hospital around 3.50pm.
Lynette died from head injuries.
Mr Chan said: "The whole family is in shock... I am still in denial. I know that it will eventually hit me and I will break down, but I don't know when."
He said the last time he spoke to Lynette was on Sunday night, when the family were having a meal together.
Describing her as a private person, Mr Chan said she was closest to her youngest brother and her grandmother.
Other family members said as the eldest, she was a mature girl who took care of her grandmother, 78.
Mr Chan said: "She has the same interests as her brother... they both love to game and they love anime. They would both game together every day, and she would also go to gaming centres and her friend's house to play games."
He added: "She was the least of my worries because she was responsible and she did not stay out late.
"She kept me informed of her whereabouts."
She was an avid reader and particularly enjoyed fantasy books such as the Harry Potter and Percy Jackson series.
At school, Lynette was the hydroponics chairman of the school's Green Ambassadors Club, where she was in charge of checking the health and the water level of the plants.
Her senior Loo Juan, 18, a former member of the club who was at her wake yesterday, said she enjoyed the club activities very much.
The second-year student said: "She was a shy and quiet girl, but she became much more confident after she took up the post as a chairperson. Her death is a great loss."
This article was first published in The New Paper. Permission required for reproduction.