She could be prosecuted. They don't prosecute in every case. It depends.
The trouble is that if she doesn't put her hands up now and they discover it later which could well happen then the sentence would be far worse.
It is probably 50-50. It would depend how much of a problem she has been for the police in the past with her allegations. If she is somebody who keeps the police on speed dial then a prosecution is more likely.
That said, if she puts her hands up now the chances of prosecution or a more lenient sentence are greater than if she is disbelieved later.
You have to bear in mind that this whole issue is coming to public attention increasingly as the public are realising that false allegations are, in fact, rife in the UK whatever they read in the papers.
That said, there are far more false allegations than genuine reports of sexual offences so her chances of escaping are fairly high if she confesses early.
Can I clarify anything for you?