How do I motivate my MIL to move more?

That's good news! Will it be possible to arrange for someone to check in on her daily, at least to begin with? Maybe her GP might be able to suggest a service that could do that. When do you expect her to be ready to go home?

I actually think I found the answer! I started discussing with her about going home to her house (which is 3 hours away). With a few aids such as a bath bench and odds and ends, she should be able to go home to her husband. He is a truck driver and is only home a few times a week, but her Parkinson disease is not advanced enough to limit her. Thank you for your response though!

I would do two things.

1. Ask her PT for a daily exercise plan, printed out on pages that you can pin where she can see it. I admit I did also do a calendar with ticks and smiley faces for days when we'd done the prescribed exercises - we? What do I mean, we? But that's how it felt... - but your MIL might not care for that approach. In which case she might poke you in the eye, and you might want to try a different reward scheme, like a celebratory dry sherry. But then again we were doing exercises for falls prevention and for hand/wrist rehabilitation, and your MIL has much more pain to cope with in larger limbs. So...

2. Manage your expectations. Activity, movement, exercise are all highly desirable, but temper your enthusiasm with empathy. Encourage, assist, support. Don't force.

Does she have supervision throughout the day? Since she cooperates when asked to move, are you sure she remembers to do it? Has she been assessed to see what is impacting her initiative to move more? Does she have pain that is limiting her movements? I would suspect that she's afraid of falling again. I would think that building her strength and flexibility would help her body and make her more confident.

I hope others where who are familiar with Parkinson's will chime in. I think that the ability to walk is affected with that condition. What does her doctor and the therapist say about it?