I had something like this with dd around the same age.
There were 2 classes of 30 pupils each in her year group at primary school
Dds class was really lovely
The other class reduced to 20 children by the time they started year 3
The children were moved between classes so each class had 25 children each.
one child was moved from the lower numbered class to her class. Within days this 8year old was showing that she had a problem. She was obsessed with death and watching someone die. Brought knives into school and targeted dd
DD was frightened of this child but the school refused to do anything about this child’s behaviour and issues. I was told they couldn’t expel her as she was in the catchment area for the school. (Bit of a dig at me and our housing situation which is too long to go into)
I ended up pulling dd out of the school. Within a few weeks someone else had pulled their child out of the school as this girl had started to target their dc
Going into year 5 there were only 12 pupils left in that class
Don’t know what happened but it was at this stage that this girl was taken out of school. Don’t know if her parents moved house or they had been persuaded to remove her because the situation was untenable
I always wonder where she is now and what happened to her. Just for safety’s sake