Please don't sneeze at the post who suggested eating wild fish because actually fish is good for our brains and we should all be eating one portion of oily fish each week and one portion of white fish each week. Studies really have shown people feel better. So the fish don't necessarily have to be wild. But canned sardines in tomatoe sauce etc, very good source for feeling good. Try fish that she does like. It won't be immediate I'm affraid, but in time and it best in conjunction with everything good.
She is no longer Catholic you say and wont talk to her friend. But would she perhaps talk to a priest if he came to your home and you were out of the room so that she could openly talk and openly share how she is right now with him as some priests are very good listeners and will 'walk' with whatever decision she makes and stay with her throughout and that in time might encourage back to the faith? She is angry and she is hurting. She mayn't be able to say why and the what for's but a priest who listens well, that would not matter for they know how to be there for you when its needed. Failing your wife talking to the Priest, it is something you can do for yourself and really talk I mean. Not clever words, just be totally open with him and let him guide you. It really helps trust me.
God is with you both right now. Ps you can privately pray for your wife that is something you can do for her and continue to be her friend as well as her husband as hard as it gets but try not to force her into anything if you can but be at her side but finding time to laugh and laugh with her.