god Donna is just. She’s so important. She’s old enough to not need the Doctor. She’s not emotionally dependent on him. They’re friends who love each other but it’s not some sort of living crutch for either of them. 

She recognizes that he needs someone to watch him, keep him from going too far. She says as much at the end of ‘The Runaway Bride’. And she does that, not because she feels obligated or because she thinks that it’s ‘not the real him’ when he’s like that. She does it out of friendship, and that’s that.

That’s why I love her as a companion. There’s no weird ‘well I’ve projected my hope and my love onto this pedestal of a person,’ she sees him and treats him like any other bloke. He’s just a guy with a time machine and a hero complex, she’s not scared of him and she doesn’t worship him. It’s about as healthy as DW has ever had when it comes to how people should treat each other.