I like that idea, in that case I would think that he didn't actually expect that she was a vampire though. At least maybe not until the graves started getting dug up. That could be the reason he came to talk to her. 

I really like how you wrote it in your post though. Him kneeling and telling her that it would be alright. I would think that anyone who started questioning if it was Elizabeth he would deter as well.

(Elizabeth drank from Jonathan?) I would think it would be a conscious thing as well, let unless you know what you're doing and how to stop it the venom sets in as soon as their fangs leave the bite. It what take years to master control and a lot of trail and pain to the victims I would think. It would also explain why vampires try to drain the victims completely so they don't turn.

Haha well we just started if you want to change Elizabeth but we still have things to chance and make the main more interesting. The others have all their history written out all the way.