An unbeatable fortress of a singe vampire?

I thought if I seal a vampire in a 3x3 room with a chair, my fortress becomes unbeatable and I also get a free bookkeeper as a bonus.

When I went to this plan for the first time, the vampire worn off all her clothes, threw a tantrum and dead painfully in her cave.

Before going for it for the second time, what should get prepared for? Ok, I'll put a whole stockpile of clothes in the cave in advance. What else?