A memorial service is being planned for Tuesday for the 15-year-old girl killed while riding her bike with family for charity.

Monday the students who knew Rachel Giblin were in mourning along with her family as investigators try to provide them all with answers.

It was an awful way to start the week at Country Day School. Giblin had just begun her freshman year. Monday students and teachers held a tribute to remember Giblin and support her older brother, Tommy, who is a senior and was hurt in the accident.

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Rachel Giblin was killed while participating in a charity bike ride.

Rachel and her brother were riding tandem for a Multiple Sclerosis charity ride when a pick up truck collided with the bike and killed Rachel. Tommy was hurt along with his mother.

“It's hard for them to see teachers cry, but we're doing it, said student advisor Imana Legette.  

Legette said Giblin always talked about her love of tennis and horses.

She would tell me about the temperament of horses (and) she would say why can't they just be nice? Why can't the horse always be nice? And I think that was her heart. Her heart was so kind.

The accident happened on US 15 in Marlboro County Saturday, about 90 miles northwest of the group's destination in Myrtle Beach.

Investigators said the driver and cyclists were going in the same direction on the two lane road.

Police are still trying to figure out how the accident happened.

“Whether the bicycle was out in the lane, or whether the truck was not yielding the right of the way to the bicycle, both of those are still in play,” an investigator said.

Anne Marie McDermott, with the MS Society, said the group has been riding the route for 14 years without an incident.

“We evaluate every aspect of the bike tour and we will continue to, butt right now our focus is on the family and their grief and doing what ever we can for them,” McDermott said.

Highway patrol officers said Rudy Robinson from Hartsville, South Carolina was behind the wheel of the truck.

6NEWS spoke with his wife Monday. She said she and her husband are in shock and their hearts go out to the Giblin family.

Investigators hope to wrap up their investigation by Thursday and will decide whether Robinson will be charged.