Yes all unsecured debt has to be included, my husbund has a joint loan with myself and i was advised by my iva company that i had to include it as it was in my name aswell .
If that is your wife's only liability, it may be possible for your IVA to bind that creditor to just accept a dividend from your IVA and not to pursue your wife separately - but that would be dependent upon her own circusmtances, and whether she could afford to continue to service the ongoing repayments on that debt.
Best to take advice on this matter from an insolvency practitioner, as you do not want to leave your wife with a problem she could not deal with.