Here’s something to point out to her:
Mental illness is NOT an excuse to be abusive/controlling. If he is not mentally well enough to not be abusive, he needs to not be in a relationship until he has dealt with that issue through whatever combination of drugs and therapy work best for him.
Repeat as necessary.
What kind of weird answer is that? 
Sorry, I just thought I was being hilarious. Because I AM male or female, see? But not everyone in the story is. I tried to make it easier by assigning everyone a gender so I could just say he/her.
Maggie the Ocelot, this is actually something I’m trying to find words for. My circle of friends say “he’s crazy, she needs to break up with him!” but I think that mentally ill people deserve love just like anyone else deserves love. Also just like everyone else, if they have an issue that’s causing problems in the relationship, they need to work toward making it better.
So I’d rather say something like “he has some obvious mental health issues and they seem to be causing you stress. Is he seeing someone to get properly treated?” But, you know, better.
Y’know, it makes a big difference whether you’re a bloke trying to give advice to a woman with (what you perceive as) relationship difficulties, vs a woman attempting to do the same.
Why are you being so coy? Your gender makes a huge difference re the motivations to help this person who you believe needs help.
IMHO, you should just back right off (regardless of whether you are a bloke or a sheila) and be there on the chance she needs support if and or when her marriage falls apart.
In the meantime, stop being so dickish. 
Who’s the controlling one here? 
You can’t live someone else’s life.