Dear Cowboy Up,
It feels to me like your wife cares deeply for you but the depression is confusing her as she most likely is having moments of feeling very sad. That makes her feel unworthy and useless and not a Person that could have feelings that are normal.
I know when I was at my lowest point and I was sad and cried alot my daughter told me it was to hard to be around someone who was so sad as it brought her emotions down and she wants to be with happy people. I was devestated and felt I should try to act happy while my heart was breaking.
I was convinced that nobody wanted to be around sad old depressed MOM.
Your wife is showing very positive signs that she will recover if she is willing to go out with you and to celebrate her birthday, she is taking care of your son and she is functioning but she truly needs some therapy IMHO.
I am glad to hear you say you won't give up on her.
I wish you peace,