Talking About Sad Things With a Person Who Has Dementia

My mother is going into an assisted living home in the next 2 weeks and she believes that my father is going with her including her dog that she loves to death but is so confused. She still thinks that my father and her dog is going with her, will she get past this or will it be a problem? She has very short term memory/Alzheimer's. I love her so much and am so scared for her.