1. Yes, you're absolutely right as to burden of proof which primarily lies on prosecution/wife's side.
2. However if she makes statements on these you have confront her on those topics as the onus then shifts on you.
3. In cross examination you have to decide very judiciously as which questions to put and which questions not.
4. Only such questions is to be put which contradicts her statements , not those which may mad her an opportunity to give explanation of her statements .
5. Burden is always on prosecution but onus shifts once to you once she states on the line of allegations and here comes the role of a seasoned lawyer to choose questions in cross examination.