I'll write what happened because I think it was terrific.
1. I came to the vampire and attacked her by wrestling upper body. It was labelled as a brawl, and she strapped her masterwork knife to the body.
2. She tried to attack me with a human tooth earring. I parried it.
3. The brawl was changed to no-quarter fight, and one of my companions started bashing the vampire with his silver morningstar. The lady, her entourage and guards remained passive.
4. I grabbed the vampire's knife, and the next attack with earring was immediately blocked by that knife.
5. I gained possession of the knife and strapped it to my body, so no one would be hurt.
6. I threw the vampire to the floor, while my companion was bashing it, which resulted in bleeding.
7. I asked the vampire to stop these silly hostilities. She agreed. My companion stopped bashing too.
8. I commented on weather and then asked for exchange of goods.
9. I traded her four clothing items covered with blood for all my meat and some gold pieces. She certainly valued the dirty rags highly. I also took the earring.
10. I drank all blood from the clothing. The vampire meanwhile dropped all items I gave her to the floor, so I took it back.
11. I started talking to the lady and asked to become a hearthperson. She agreed, which means the civ remained non hostile to me. In fact I'm now a member.
12. Then I started seeing people through walls - I became a vampire.
13. Next night I came back to the vampire to check on her. She was friendly enough and asked me if I made any good deals lately. Yes, I did.
By the way, the vampire sleeps one floor lower now, with children and servant staff, while the lady with her husband and advisers stays upstairs. May be a coincidence, may be a sign of falling from grace. Other signs are two scars on her body. Also, the ex-law-giver is very loyal to the government, in fact more so than before.
One thing I don't like is that my vampire-dwarf is slightly slower than before. Not a game breaker, but I had hoped for a speed gain rather than a loss.