23 year old daughter with burnout

My daughter has stopped communicating. She only responds with one word answers, she watches one program on loop all day. Her anxiety is so crippling she has stopped going out. Has anyone else experienced burnout to this degree. We are implementing strategies to ease her distress like low to no demand, taking her food, communicating via text and sitting with her in silence or parallel play. How did you help? What else can we do? How long did it last for you or the one you cared for?