There can be several reasons your wife has a negative attitude. One possible reason is that your spouse more naturally leans toward pessimism than optimism, so she sees problems before seeing opportunities. Tied to this is the possibility that your wife is a "detail oriented" person and tends to see what needs fixing (which can be an important strength) without seeing what there is to celebrate (which can be a problem.) Another consideration is whether your wife has had positive reinforcement in her life. Perhaps she grew up hearing a great deal of criticism or being molded by people who themselves were complainers and blamers.
Whatever the case, being transformed in one's attitude takes time and deliberate effort. If your wife were asking the question about herself I would give her some effective ways to cooperate with the Holy Spirit in order for her mind to be renewed. However, as your question is how you can help her, here are a few keys:
But what if your wife's negative attitude is aimed at you? From her perspective you never seem to handle a situation correctly. You are not praised, but consistently criticized. This is where your maturity as a believer will show forth. Instead of lashing out or withdrawing, are you able to move toward your wife and speak the truth in love to her? Let her know how her attitude is affecting you, while also being mindful to offer hope and to validate the areas where she may be right, even if her attitude is wrong.
Also, praise her often. Her cup may have endured a lifetime of emptiness, depending on her background, and you can be the one who helps to fill and revive her. This also means being honest with yourself about the ways in which you might be draining your wife. While your shortfalls are not an excuse for her negative attitude, her negative attitude is not an excuse for your shortfalls to remain unchecked. This does not mean that you are to be perfect. It means that you are to be actively growing and using even this difficult area in your marriage to cooperate with the Holy Spirit in how He wants to transform you.
Since our minds are transformed by being renewed (Romans 12:2), initiate daily devotional time with your wife where you read the Word together. Elector and I have a friend who is 90 years old. He and his wife have been married for decades, and one of the things he has practiced everyday for their entire married life is to, as he puts it, "wash her with the Word" daily. Everyday he reads the Word to his wife as just one of the ways he covers her and cares for her. It's a precious act of love and devotion on his part. Perhaps you are willing to do the same and see how your wife blossoms. And remember, it's not a matter of her blossoming for your benefit first and foremost. It's a matter of her blossoming for the glory of God, from which you will benefit.
Dr. Dawn-Marie shares a refreshing blend of professional insights and personal stories in this encouraging blog.