She will not be released after 33 years. She has a life sentence. The 33 years is how long she must wait before she can apply for parole, and there is no guarentee that she would get it even then.
When people are released on parole they are released under strict conditions that they must obey to the letter. If they do not, and even if they do, but other aspects of their behaviour causes concern they will be recalled.
John Venables, one of the children who killed James Bulger has been recalled to prison several times since his release and is in prison as I write, for breaches of parole. On the other hand the other child involved, Robert Thompson has had no further involvement with the police as he has obeyed the rules governing his parole, which will, for the rest of his life, govern everything he does.