Thanks for all the feedback, advice, and suggestions. I just wanted to add that the groom has been wonderfully supportive of my sister and explained the situation to his family. My sister had suggested that the couple put their dogs in a nearby kennel and bring a friend or an aide to assist them, but the couple declined. Five people didn't show because of the dog situation which is unfortunate. I think it just comes under the heading of not being able to please all of the people all of the time.
My sister and her husband were married on Saturday. It was the most beautiful wedding I have ever attended. About 125 guests attended and had a wonderful time.
Here I am as the maid of honor.