If she is referring to you as Candidate, it sounds like you are the one looking for the job, correct? (Just wasn't entirely sure from your post.) If so, I would take my cue from her. So as long as she's now referring to you by name, I would feel free to do the same in return with her.
You don't indicate whether she's addressing you with your first name or as Mr. So-and-so, but either way, I would stick with Ms. So-and-so in return, and avoid using her first name unless she directly says something like, "Ms. So-and-so is my mother's name. Please call me Barbara," (or whatever it might be).
Good luck. Hope you get it!