Yes, in a civil case she'd still need to prove it, although the burden of proof is lesser.
A criminal conviction requires a case to be proved beyond reasonable doubt - that is, even if the jury is 90% convinced (for example) that the defendant is guilty, the 10% of them that remains unconvinced counts as reasonable doubt, and no conviction.
In civil cases, where one person sues another for damages, the case is decided on the balance of probabilities. If the court is 51% convinced that the ex's version of events is true, she'd win the case.
That's how OJ Simpson wasn't convicted in a criminal court for murdering his wife, but was successfully sued in a civil court by her family for unlawfully killing her.
Either way, the ex would struggle to prove it was your mate who injured her - even in a civil court.
Oh, and even if he was successfully sued in a civil court, it wouldn't go on his criminal record.