At the funeral home or church service say the same thing as a non-Christian – “I’m sorry for your loss.” Depending upon the relationship you have with the widow, adding “I Love You” is appropriate.
Let her make the next move regarding the conversation. If she wants to explain what happened fine. If not, move on and let the next person in line express their condolences.
**The fact that you are there speaks volumes.**
Let your actions speak for you rather than risk saying the wrong thing.