In order to convict for manslaughter, or any other criminal offence, a jury needs to be so sure they are certain that the offence is made out.
Likley is not enough. While that seems hard here it's one of the 'golden threads' in our justice system that mitigates against the abuse of power.
Whether, the Coroner having found, but on balance of probability not certainty, that the girl was unlawfully killed leads to a further review of prospective criminal charges remains to be seen.