WOW. You did nothing wrong and that woman is not doing good rescue. A good rescue will not place a dog like in a home with small animals. (As long as they know the dog is not good with cats). I realize some foster homes do not have cats. However, in those cases they typically should tell you they do not know if the dog is ok or good with cats. I have a friend who is a foster home for a Golden Retriever rescue in Raleigh. I know they do try to make sure they know the temperament of all the dogs and if they are ok with cats or not. (She has both cats and dogs).