I can only repeat what has been said previously about introducing them on neutral territory. Maybe you could do that a few times before the dog actually moves in, so that they get used to each other - even if its only for a short while when theyre on walks. The only other thing I would suggest, is to give them all a treat when the dog arrives at home and let them settle down with them - something that takes a little while to chew so that they calm down a bit, but keep an eye to make sure no-one pinches the others chew and causes an arguement.
Also, try not to make too much of a fuss of the new dog on her own in front of the other dogs - try and make a fuss of the 3 of them at the same time (if thats possible!), so that none of them feel left out.
I'm sure you'll do fine but Good Luck anyway - keep us updated on the progress!