Superintendent Stephen Riley, head of Counter Terrorism Policing East Midlands (CTPEM), told the court two police officers attended Rhianan's home address on October 9, 2020, to seize a USB memory stick and a diary from her.
Speaking today, mum Emily said she had begged police for help in September 2020 after noticing Rhianan had developed an "unhealthy outlook on fascism".
In October 2020, CTPEM shared information with MI5, who then opened an investigation into Rhianan, the court heard.
The court was told messages were sent on WhatsApp by Rhianan about how she "wants to kill someone in the school or blow up a Jewish place of worship".
But Chesterfield Coroner's Court was told the agency had no involvement in Rhianan's arrest and charge.
