I'm a criminal barrister, I can help with this.
Did your wife give a statement to the police at the time?
Ok, so presumably the police have a photo of her cut lip and a probably a recording of the 999 call she made. The CPS can actually prosecute without a statement from her if they can argue the 999 recording is an exception to the hearsay rule i.e. that the person making a statement needs to make it in oral testimony in court.
The police and CPS cannot force your wife of going to court or making a statement.
At the first appearance (first court hearing) you can use a duty solicitor in court. He/she will fill out a trial preparation form where the relevant issue will be self-defence. It is very difficult to prosecute assault where self-defence is raised where a victim is not present - this is because you're not denying physical contact just the reason you made it.
If you this answers your question please rate me.
How long after the alleged offence did she make the 101 call?
Ok, that's good. They can't use the 101 recording as it wouldn't fall within the res gestae rule (exception to hearsay). Essentially, they will have no evidence against you if she doesn't attend court.
I think this answers your question, please rate me
Do you require further clarification?
If I've answered your question, please rate me. If not, please ask for clarification, thank you.