Especially if the label has connotations of mental instability.
I'm not saying your wife is insane, but she definitely sounds like she is suffering from chronic depression, a recognized physiological disease.
As mentioned before you said that you think she "can" she just "won't". Let me ask you this do you think she chooses to be miserable? You said she suffers from low self esteem and feelings of worthlessness. Do you think she chooses these?
Im not saying I can diagnose your wife, I'm not there. All I'm saying is that she shows a lot of the symptoms of chronic depression.
My best recommendation is to keep filling up her love tank, to the point where she believes that you do want what is best for her. Then convince her to see a therapist about her depression.
The weird thing about depression is that for some of us, it may come down to something as simple as, bad nutrition, or an easily fixable hormonal imbalance.
As is often the case, it's often more than just about sex.
You're definitely not going to cure whatever emotional road block she has in her head, she shows no willingness to do it either. So I think you should work on her overall happiness. Maybe this will put her on the path to get the help she really needs.
You can't change her, but you can create the type of environment where she feels it's the right thing to get help.
