Along with being real, like I said before, she has a lot of respect for Ash who is definitely her BFFFFF =D and he cares about her too. We can see that very clearly in the cameo episodes, as you said. They're in a different world than everyone else. Ash makes sure Misty is safe all the time. He tries to be with her as much as possible duh ;DMisty is a girl who likes girl things but she doesn't go overboard (Princess VS. Princess). She's not vain or shallow (The Stunspore Detour). She loves her friends, Pokemon and life. That's the real Misty, and I think as soon as Ash stared seeing that more is when they started to become closer friends. Whenever they reunite in a cameo episode it almost seems like they're on a whole other plain.
I LOVE THAT COUPLE SO MUCH!
*POKESHIPPING HUGGLE (which is the best kinda huggle everrr)*