A letter sent to all parents at Hermitage Academy described the first year pupil as a “cherished member of Arran House”.
It stated: “Her tragic loss will be felt by all staff and pupils.”
An online fund-raiser has been set up by a family friend to give the 11-year-old a “beautiful farewell”.
Organiser Christina Blair wrote: “Olivia was a bright, loving, and unforgettable soul who touched the hearts of everyone who knew her. “
Jackie Baillie, the local MSP for Dumbarton, said her thoughts were with Oliva’s family and friends.
She added: “I am advised by Police Scotland that the investigation into the cause of Olivia’s tragic death is still ongoing and is currently being treated as unexplained.
“It is important that we get answers on what caused her death in order to ensure this unthinkable tragedy cannot be repeated.”
Argyll and Bute Council said it was providing support to Olivia’s family along with staff and pupils at the school.