How do you get an 85-year-old woman to regain muscle mass?

If she doesn't WANTto do it HOW CAN we get them to do it??...I need an answer too!.My 78yr.old Mom (with ALZ.'s,depression &severe Arthritis,doen't seem to WANT to get better. I'm at my wits end-cause I know if she doesn't do something soon she'll be immobile/wheelchair bound.She's had Dr.ordered physical therapy-then dropped it-she said it wasn't helping her,..and refused to see a psychiatrist~:(
(I-know),it's been proven no matter how old you get,it's still possible to build muscle strength-and improve mobility.We just CAN'T force someone to WANT to get better.