This is a very random and probably total impractical suggestion, but is there any way you could video your wife's behaviour when she berates your daughter?
I know this seems strange, but given her OCD issues is seems as if she cannot control her impulses terribly well, and perhaps seeing herself on screen, talking to your daughter in such an appalling way may help her to realise the damage she is doing.
I'm so sorry you're having to deal with this, to be honest this is abusive behaviour and you do need to come up with a strategy to cope otherwise it will just escalate. Your poor little girl.
As you say, a formal intervention may be what is needed, and I think you need to seek professional advice on this. If your wife has been diagnosed with OCD, does she see someone to help her manage it?
You must take action however, if my DH spoke to our DD like this I'm afraid to say I'd leave him, and restrict access to our daughter until he learnt to manage his behaviour.
I'm so sorry once again. Please give your little girl extra hugs, it must be bewildering for her to be spoken to like that by her mum.