Has the dog been checked out for hip dyplasia? Spinal stenosis? any other health issues?
Most "accidents" will happen when a dog is sleeping, or passes gas etc, it is completely uncontrolable so no amount of training is going to help. You can lessen the possibilities of accidents by feeding the dog dry dog food and take it on frequent walks (once checked out by a vet for hip or spine problems) and you can diaper your dog while it is sleeping or walking around the house.
You do need to be aware that the other dogs in yourcare might react negatively to the new dog and may even get aggressive towards it or shun it due to its health issues.

You are a better person than I ever could be. I don't think there is any way I would bring a dog into my house with that specific problem. One thing if it happens due to old age or what ever but to start with it knowingly it's more than I could do. But good for you. The world needs more people like you.!!!

thanks mazer - that's helpful. The lady is saying that the dog is not incontinent - that i misinterpreted what she said. Could be right. I was trying to read through the lines - don't trust anybody - lol.

i'll be picking her up on wednesday.