I've not notice this myself but my dad has. He says that sometimes mom (pwd) will twitch a lot while sleeping and then wake up and start meandering around. I think it's not subtle or like REM sleep type twitching if my dad is bringing it up, but he can't describe it as anything other than twitching.

This seems to happen around 1 to 5 am, mom goes to bed around 8pm if that's any help. 

I don't trust her doctor so I'm seeing if anyone might have some suggestions on what it could be or what to look into next. My expectation is to have more information on the phenomenon before bringing it to the doctor so she can't just hand-wave it off, if it's something more serious.

It could be periodic limb movement disorder.  Does she have restless leg syndrome?  The two disorders are related, and contribute to poor sleep.    My spouse ( no dementia) has both, and certain medications treat both. In his case, he also has sleep apnea.  He sleeps much better now that he’s got a BPAP machine.

Your mom might not be able to deal with the sleep apnea machine even if you could  get her through the sleep study appointment.  However medication could still help the movements. 

Thank you! I'm not sure she has restless legs syndrome. Is that something you can get at any stage of life? I think it's a whole body shake, not just limbs but I will inquire more from dad when he gets home from work tonight. 

She snores when she sleeps usually so I suppose that sleep apnea is a possibility. Dad has a CPAP of some type and mom's terrified of it sometimes. As you say, I'm doubtful she'd tolerate having her own.