Sorry guys, I should have updated earlier!
After we'd both had a couple of days to cool off, we sat down and had a long chat about it. She fully admitted she started the fight deliberately, as she "wanted to see if she still cared when I was angry/upset with her", which I'm sure you'll agree is a **** "excuse" (she has said a few times before that the anti-depressants she's on make her feel nothing at all).
I made it very clear that it wasn't acceptable, she'd crossed a line, and that I was very seriously thinking of ending the relationship at that point - told her that if she didn't show genuine effort to start dealing with her mental health within 6 months (or if it happens again) then I'd be looking at our options for separating. I made sure she knew I'd be fully supportive if she made the effort, but like you guys said,
she needs to want it and to be the one driving it. She agreed that was reasonable, and does accept that she was out of order, and does need help.
She has spoken to her GP to arrange a medication review - she did initially say about just coming off the anti-depressants altogether, but I managed to talk her out of that idea! She did also say she was going to ask about counselling, although I don't know if she's done that yet.
I have reminded her about it a few times; I don't want to end up nagging her about it, but I also don't want it to end up getting just brushed aside and pretend everything is fine again, so a careful balancing act!
Other than that, day to day has been almost the same, but with some subtle improvements. She's definitely been putting in a bit more effort to do her bit around the house; doing more cleaning/tidying rather than just moaning about some "mess" I've not had the time/energy to sort (I've even had some nice surprise meals cooked for me
).
It remains to be seen if that lasts, or it's just a short-term thing, but I'm going to be open-minded and give her the benefit of the doubt; she's definitely trying, it's just whether she keeps on trying, or decides it's too much hard work again, and it's easier just to let me pick up the slack.