"even if she spends ages fussing and chatting to him before she tries to get the head collar on"
If she's fussing and chatting to him, she is no longer ignoring him. The head collar bit happens after all the ignoring and should take minutes.
I have tried the ignoring thing with a hard-to-catch horse and was told it had to be 'interesting looking' ignoring (to the horse)!
So the first morning, I took the wheelbarrow, put a couple of empty buckets on it and went poo picking. While I poo picked, I clattered things around a lot, occasionally dropping the buckets and generally making a performance of it. Periodically he'd close in for a better look, but when he did I didn't look at him, just swung my head away and 'turned my hindquarters' on him, positioning my back between him and the action. Yes, I do know what I must have looked like!!!! 
Once I'd done about 20 minutes, I left. Came back that evening, this time with half an apple in my pocket. Did exactly the same thing, this time when I left, I left eating the apple (that is, me eating the apple).
Second day, morning and evening, did exactly the same thing as the first evening, and on both occasions he walked to the gate.
Third day, we got the gate and (holding the apple in my teeth) I put his head collar on, led him out, gave him the half apple out my teeth, brought him in and groomed him and turned him out.
I have no idea if it was important, but all the way through the poo-picking, the acting, the apple eating, and the eventual head collaring I didn't speak to him. Not once. Also, when i turned him back out, I led him right up the field and just left him very quietly with no reward or pat.
By the fourth day onwards, I only had to poo-pick for 10 minutes and shortly after we stopped even that, just the walk and the apple eating would do it.
I've only ever had to try this with one horse, and it had a permanent (as far as I know) effect on him, so have no idea if it would work on others. Nor can I claim it to be my idea. A friend suggested it.
It was a labour of love. I don't like apples.
Good luck.