A man is helping police with their inquiries in relation to the incident.
Officers earlier sealed off the scene and a full investigation is underway, added the police spokeswoman.
Local people say Esther, from Cwmparc, was on her way to collect her results at Treorchy Comprehensive School at the bottom of the hill when she was in collision with a council refuse vehicle at the junction of Conway Road and Chepstow Road.
Her head teacher Bethan Guilfoyle described Esther as an extremely likeable and very popular pupil.
Mrs Guilfoyle said she was very much into performing arts.
She said Esther was quiet, unassuming and lovely, she did well at school and overall was a delightful young lady who never put a foot wrong and had good attendance.
Her older brother Michael left the school a few years ago and her sister Rebecca is due to join Treorchy comprehensive next month.
Esther lived with her father Laurie, her brother and sister.
One of Esther's neighbours, Mrs Shepherd, said she was a "lovely girl".
"She was always singing and she played the recorder, she liked her music. She was very outgoing, you'd see her dancing around to her music, a typical kid of that age," she said.
"We'll miss her being around, you just can't accept what's happened, it's horrible, an awful thing to have happened."
A spokesman for Rhondda Cynon Taf council confirmed that some staff members were being interviewed over the girl's death.
"We are aware of the situation. It is one of our vehicles. We have staff involved and they are with police at the moment," he added.
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