Don't post anything through her letterbox. Is she on FB or twitter? Add her as a friend. You could share some things from women's aid/the police on your own profile and hope she sees them. I share stuff like that all the time so it would be be weird for that to pop up on her newsfeed as long as you don't tag her in anything.
But agree with being there for her. When she talks, just let her talk and if she asks what you think then try and gently say you think it sounds abusive and maybe she could call women's aid for their opinion.
I don't think it's depression for a number of reasons. I have worked with people who are depressed but of course I could be wrong.
It's just comments about how useless she is and how things must be her fault, even when it's obviously not.
She makes passing comments about her husband and they are quite concerning. Things like he stops her doing things or reminds her that she's terrible at finishing projects so she shouldn't bother starting.
Lots of little things that just give me an uneasy feeling.
Tough one, chances are if you said anything to her she would not take much notice. I think all you can do is be there for her when she needs you, chances are eventually she will realise what is happening, when you are in that kind of relationship it's not alway obvious to the victim that they are in a abusive relationship.
Just be there as a friend send be ready to help her if she makes the step to leave him.
I think I'd start with "Is everything OK?". She'll either open up or say it's all fine. If the latter, just let it go. You can't force confidences but the fact that you asked might prompt her later on.
I'm in the same boat, i know for sure he is controlling and very sure he's emotionally abusing her too. I can't do more than talk to her,well more often listen. I know she's not ready to leave but we talked about what ifs and how would it work, benefits,entitlements etc so she has that knowledge. She does know that if things turn shit there's always room at mines for her and her little girl. Dunno what will happen and I can't make her leave,but I am here for her and making her aware of everything that would empower her her to leAve, ot the least how awesome she is.
She'll open up when she's ready. And I agree she's lucky to have a friend like you. Just be patient, listen, ask a few non confrontational/non critical questions. She'll open up when she feels able, just be there for her.