As it was a joint debt your wife was and is legally responsible for the whole debt once you became insolvent -- only you are absolved due to the IVA. They are within their rights and are likely to request that she settles the debt.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk