How strange. Does lesser restoration remove the knocked down status as well as paralysed? I feel like I have seen knocked down before, eg when being attacked by the bullette but don't recall having paid a lot of attention to it. I'll look out in future.
This party doesn't have a way to cast Lesser Restoration on her, so I unfortunately can't check.
I have managed to narrow the issue down, though; I had an earlier save, which I could use to confirm that she wasn't Knocked Down the entire time. But if I start a fight in the area outside (easily done by failing to read the mind of Guex, the tiefling that is struggling with the training dummy), as soon as the fight is over, she is knocked down. Since I don't pull the fight into the shed, I haven't been able to see when she falls down - I just saw her enter a combat stance, and then the camera hijacked me.
I suspect that when she should otherwise have joined the fight, she gets "Knocked Down" instead, in order to keep her lying in her place, but this effect never seems to wear off and is re-applied again and again. It is also not cleared on a long rest.
Also, when I tested this, I turned off all my mods that could have anything to do with mechanics, only using UI and cosmetic mods that should not reasonably result in anything like this.