I'll be honest, I think all four approaches stem from your feelings of frustration with the situation but probably not the best approach if you still want to work on building your marriage.
I think you may be on to something with suggesting therapy, but not as a threat demanding specific results. Therapy just doesn't work that way. I would probably approach it with more empathy. What is it you really want after all? If it's for her to find out what is causing her to withdraw she will need to go into it with a positive attitude wanting to make those changes for herself because she's not happy. The problem lies in that if she thinks everything is fine with herself and you are just expecting too much, therapy won't be the answer. She will need to be invested in the concept...like that old joke:
How many therapists does it take to change a light bulb?
One. But only if the light bulb really wants to change.
Have you thought about marriage counseling? I haven't been myself but I'm thinking it might be helpful to discuss the issues with a third party that could add some insight. Your wife may be in a comfort zone with you where she's not really seeing her actions as a problem but rather your expectations too high. A marriage counselor may be able to put things into better perspective. If there are things bothering her that she's been keeping to herself, it may open up that dialog also.
In the meantime, do you have anyone that can watch your son for an evening? It sounds like you could both use some uninterrupted time together to either take a walk and talk or do something fun with each other.
I don't know...after the survivor thing you are probably feeling pretty unloved/unappreciated so maybe that discussion needs to happen first...how it is making you feel and that you feel you are drifting apart and are lonely in the marriage, etc. Any conversation will be more effective if you talk about your feelings vs. putting her on the defensive where she feels the need to defend herself rather than listen to you.
I don't know how deeply I'd read into her having close friends. I have several but it doesn't mean I'm opening up to them or closer to them than my husband. They mainly like to vent to me and ask for my input...but I'm still more of the keep to myself type. On the other hand, sometimes it's just easier to talk to other women about things.