Mac Pro 2013 12.7.6 will not unlock in Apple Remote Desktop

Hi all. My wife's MacPro 12.7.6 is locked in Apple Remote Desktop (I swear this happened randomly) and I can't unlock it. I can see it's locked in ARD when I try to control it. I try lock and unlock and restart - no luck. I can SSH to it but I've tried a few commands without luck they don't seem to run. Is there a file I can delete? I believe this is the Curtain process? Please - any tips will really help. Thank you.