Finding it hard to keep up with this thread but.....
Whether what Helen did was reasonable self defence or whatever is going to be based on the details of who went for who when, where they were standing, and other details which it wasn't possible to tell by listening to the episode.
I agree with Wannabe though that I'm not at all sure Helen was defending herself when she stabbed Rob. It sounded very much like she had completely lost it - there was fear there of course, but also rage, and as we have said previously, she seemed positively disappointed when Kirsty said he was still breathing.
However I do think the months of abuse stand her in good stead for a defence of diminished responsibility and it doesn't matter that she has previously denied abuse to friends and family - minimising it to others would be fairly normal in the circumstances I would think.