Is it illegal to deny guilt after accepting a police caution?

[jeremy101]

A mother posted malicious lies on the internet. It was traced back to her computer, she admitted her guilt to the police, and received a police caution.
She has since told the magistrate's court and the family court that in fact she didn't do it.
Is she committing a criminal offence by doing this? And if she sticks to this new story can she be referred back to the police to be charged, as you can only receive a caution if you admit guilt?

Also, she has not removed these posts. The police say they have no power to force her to remove them.
Is this really true?

[jaycube]

Anything can be possible may be she is trying to defend herself and remove all those posts from the internet or police can also force her to remove the malicious content, only god knows the truth.

[jeremy101]

only god knows the truth.

Sorry, I didn't mean is it true that she did it. The point is that she admitted it by accepting a police caution. So in the eyes of the law she did it.
I mean is it true that the police have no powers to make someone remove comments from the internet?
And is it a criminal offence to say in court that you are not guilty after you have accepted a caution? And can she be charged with perjury or contempt of court or some other offence even if the judge at the time chose not to?