It would be kind of hard to tell her the thing she is missing in her life that used to make her happy is me. I bet she would find that hard to believe.
I wouldn't advise you to tell her that.
It sounds as if your W not only depended on you to make her happy, but she allowed herself to be defined by you. She isn't happy with herself so she blames you. I'm not certain that you are the one to explain that to her. Not only would she find it hard to believe, but she would resent it.
I don't know what it might take to get a fire under her, but as long as she can point a finger at you and say you're to blame for everything negative in her life, then she will never grow as a person.
I'm not just trying to find words to say here...I really believe she needs to learn to be "responsible" for her own happiness. And, you need to refuse to take the responsibility for her happiness! Can you see that you have been taking the responsibility for that?
I understand that you feel bad about being gone so much in the past and all that revolved around it, but trying to make amends by becoming her happiness will not hold up. There are some things that a person has to learn for themselves or have an outside person guide them. I think this is one of those things.
It's not being mean, but it may be difficult, b/c you want to help her so much. It's like applying tough love. If truth be known, there have been many M's to come to an end simply b/c the W or H was trying to find happiness.....and the problem was the individual, not their S.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!