Now that's the other side of the scale: toxic negativity. The key here is to reach for a balance and accepting, that you have both positive and negative thoughts, but you always should seek for the balance. Suppressing either positive or negative emotions will lead to a bad health. I'm afraid you have to wait until your wife is willing to seek help for herself, because change starts by accepting your own need of help. Maybe you could suggest her to seek therapy to deal her issues