Good luck mixing your sows. As others have said, give as much space as possible (better to give neutral ground, but I understand that's not possible). I'd try and mix at late afternoon/evening feeding (whichever you do), so that darkness comes soon and hopefully calms the situation.
Plenty of food, widely spread, when you mix them. Inevitably, the newcomer will spend the evening outdoors, but they should be sorted by the next day - but still expect squabbling over food and spread widely to ensure both get their fair share.
One word of warning that you might not want to hear: I had my best sow (newly-weaned) killed by a heart attack brought on by an over-aggressive sow (later found she had polycystic ovaries). I used to accept initial sow squabbles as something that just happened, but would blow over. Now I stay with the sows until I'm absolutely sure they are settled. Good luck, Liz