I was thinking Pansy, actually, because you trust her. Although she isn't as experienced, and I have no idea how she would be as a teacher.

Maybe Madam Pomfrey would be good then, if the two of you can find some excuse to get away? I dunno, going on an herb-gathering expedition for supplies for the Hospital Wing or something, since she's taking you on as a likely student to mentor. I know, I'm grasping at straws, but maybe? She'd also be good because she could deal with any splinches that come up.