How can we make having my mother-in-law live with us work?

My husband and I were just married last month. His elderly mom is 82 years old and lives with us. She had open heart surgery last summer to repair some valves that were leaking. After that I took care of her and all medications and doctor appointments. As she was feeling better she wanted to take over doing these things herself. Let me also say that she is highly depressed but will not take any medications for this! She gives us a hard time about everything! She lies to us and we catch her all the time! She has been messing up her appointments and stopped taking most of her medications! Usually every Friday there is a illness going on, most of which have been checked by the doctor and nothing was found! But usually by Monday, when a doctor is available, she says she is fine!! She helps with nothing around the house but will get up in the morning and take off on the bus for the day doing whatever!! It has caused so much tension between my husband and myself! I don't know what to do anymore???