Thank you all for your help. I'm not sure if Winnie falling in the pond last Sunday had any effect, but they were a lot better during the week, apart from the odd tantrum from Winnie before bedtime, which I am assuming is because Tilly was staying out late.
Tilly stuck her head in the hen house most nights this week then went to her temp house, so I removed that yesterday and last night after a dozen sorties she went in and stayed in the house.
Tonight she got the usual pecking before bedtime because she wasn't in bed, but went in to the house a bit later and hasn't been out since.
I should point out over the last ten days although the pecking seems vicious and Tilly is totally dominated (although she does peck Winnie's legs when getting pecked sometimes) there's only been one feather found in the run. It looked awful but fingers crossed no real harm.
I think the two weeks seeing each other seperated helped, and it was no where near as bad as I thought, and all the worrying stuff was over within two days. I'm conscious that I started this thread because there's hardly any advice out there for adding one to one, I've done it twice now and the easiest one was last time when I put the new one in the hen house at night, they got over it in a day. This time was harder because it appeared more extreme, that could be because of the personalities involved, or it may have just been easier to put the new one in at night -- as everyone says, each situation and chicken is different.
Again, thank you all for your help.
Now, where's the thread on adding a third hen to two established.........