"If I didn't believe you were still a person, we would be having a very different conversation."

Probably one with threats and lightsabers. Or at least a whole lot of cursing. She still can't say she likes Vader exactly, but she doesn't hate him. That's still a surprise.

"It's still strange to think that you'd help me, but I do appreciate it."

Even if she feels a little bit like the worst Jedi ever for striking a truce with Darth Vader -- but if Obi-Wan Kenobi could do the same, she certainly could. She had no personal grudge, after all. Things might get awkward if Luke ever decided he needed her help to stand against his father, but she'd cross that bridge when she came to it.