How do motivate my daughter to do something with her life?

My 28 year old daughter and her 7 year old daughter have been living with me and her stepdad for the past year and a half. She was living with a boyfriend but they broke up. She only recently got a part-time job as a server in a restuarant. She lives off the system and us. We are coming on hard times ourselves and can't support her any longer. I can't put her out because of my granddaughter. We are at our wits end!