Only she could say, of course, why she chose to remember him in this way -- although she may not know herself. Sometimes our motives are hidden or unclear even to ourselves; the Psalmist asked God to "Forgive my hidden faults" (Psalm 19:12).
From what you say, however, I suspect one reason could be her regret over the past. In other words, perhaps she was trying to make up for the way they treated each other when he was alive. In an obscure kind of way, she may even have been trying to apologize for the failures of the past, and let others know that she really did love him, in spite of their problems.
Instead of dwelling on this, however, I hope you and other members of her family will reach out to her and assure her of your love and concern. She can't change the past, and neither can you, but you can let her know you care for her. Some of the saddest words in the Bible are these: "People have heard my groaning, but there is no one to comfort me" (Lamentations 1:21).
In addition, ask God to help you point her to the comfort and hope we have in Christ. Because of His death and resurrection we can have hope -- hope for this life, and hope for the life to come. When we know Him, the Bible says, "weeping may remain for a night, but rejoicing comes in the morning" (Psalm 30:5).