Anyone can have a copy of a death certificate; that doesn't make her a special representative or even his executor. And why would she have "all his w2s etc?" well, it seems likely someone would have had to give that to her, so someone has been wrapping up his household? Is that someone authorizing her to handle having the taxes filed? Ask her who is authorized to sign the return, and have her prove that person is authorized. Remember your due diligence.