I would have a problem if she is the only person performing the audit -however if others were to help out I wouldnt have a problem with it as long as another person signed off on everything. A really good friend of mine was our Treas and I found that she was missing deposits, etc.-- I had no choice but to be honest and turned it over the BOE. I lost a friend but I maintained by integrity but I agree with Serendipity that it would be unlikely that a wife would tell on a hubby. I'm sure that it is all on the up and up but you dont want to take the chance of someone coming back later and claiming otherwise.
I would certainly consider it a conflict of interest. As for her being the only one to be on the auditing committee, well then that is just ridiculous and you might as well not even bother doing the audit. Let's face it, if hubby was up to no good and taking money is the wife really going to report him and have him arrested?