FY, I am so very sorry about your dog. They become our children and love us unconditionally and it hurts deeply when we have to make the choice of putting them down. Please remember the goods times w/your pet and know that you and your wife did everything humanly possible for her. You both gave her the gift of helping her reach the other side w/o suffering longer than she had to.
In time, you and your wife may opt to get another little bundle of joy. But, that is down the road and you both will need to grieve the loss before that can happen. Give yourselves plenty of time to revisit those wonderful memories of her and when the time is right, a little bundle of joy will venture on to your path for you to love. The man upstairs has a way of doing this to those who have lost pets.
Take care of yourself.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.