Montana plays loosie-goosey with selling death certificates, but in many states they are denied to non-relatives (which may not be the case here, although how do we know they were still married, if ever?).  On the other hand, in Arizona you can be appointed personal representative with just an affidavit; a death certificate isn't required.  

I would listen to her story and if I were looking for new clients (I'm not) and it sounded reasonable, give her an estimate and ask for a retainer.  I have had several clients who have stayed married even while living apart for many years, sometimes with a new domestic partner.  They do it to remain eligible for insurance and/or pension benefits, among other reasons.  Occasionally it's religious.  But I have known them when they were still filing joint returns, or I have known their close family members.  

Trust, but verify.