How can i get my landlord to let me keep my unauthorized dog?

I just got her as a therapy dog because I have problems being alone at night. I have Post traumatic stress disorder, major depression and hyper vigilance. My husband is deployed right now, so my state of mind was not right until I got her. I can sleep at night now knowing she's there to protect me and my kids. Any information that can help me in this matter will be greatly appreciated.