Pet Xinroch is very awesome
Why did it say "You should perhaps move a bit closer" in the first screenshot?
An easier way to get Sherry to lose some limbs than leprosy is to set traps for her... I usually lay about 4 adamantine traps in a row in a hallway and let her get stuck in them. You'll have to lay them down multiple times and repair them because she will usually break them and get through, but eventually she's likely to lose a limb or two.
If you're lucky she may even get both arms stuck in the trap and then you can attack her while she's helpless. That only happened to me once. That's very risky though because there's no way to know for sure - once I thought she was stuck so I went up to attack and as soon as I approached she injured me badly. She still couldn't move so I was able to run away but she nearly one-shotted me even while her legs were stuck.