Her mother later discovered the messages and contacted the Child Exploitation and Online Protection (CEOP) Centre, part of the National Crime Agencyy* (NCA), which advised her to report them to the police.
“They have discretion not to take formal action if it isn’t in the public interest to do so. Police are encouraged to take a common sense approach that does not criminalise children unnecessarily.”
So from reading the article you'd finally sent, (bit difficult for me to previously answer your questions when I didn't have the case you were referring to), although it seems unfair and unjust there are elements to this that need to be considered.
CEOP were contacted. The police have a duty of care to inform the parent that there was a "possibility" the child could face charges. In an event that the child was part of a child exploitation ring, which isn't this case in this situation, there could be charges brought. For example, it's been known that in these exploitation rings children become a part of distributing images and become involved in the process in a criminal manor.
Just because the police force said there was a possibility she could face charges, doesn't necessarily mean she did. I'm sure that when the police rule out the possibility of the child being a part of an exploitation ring, any form of indication that she may be "charged" become void.
It's about seeing the bigger picture from a legal perspective and ruling out possibilities.
I'm sure you won't agree with anything I have to say as you seem hellbent on straight up blaming the system without looking at the bigger picture.
I would like to see the end result of that case.