We ordered a headstone for my sisters' grave and among the wording we chose "...a loving wife of the late....." When they sent a proof of the template, they had changed it to "...a loving wife to the late....." Which of them would you say is correct?
The use of 'to', in this context, indicates 'fulfilling a duty'. (e.g. as in "housekeeper to the bishop" or "butler to Lord and Lady Briggs").
While your sister may well have 'fulfilled her wifely duties' to her husband (if you accept such a rather old-fashioned concept anyway), its probably not what you really want to say. So I'd regard 'of' as better in this case.
^ That is one context to be presumed. Another presumed context may be that you have a relationship 'to' something/someone whereas you have ownership/possession 'of' something/someone.