I feel like Donna was pretty good at side stepping his defense mechanisms, actually. She really was good for him. I about cried in "Partners in Crime" when he was panicking and she demanded point blank he tell her what he needed and stopped him panicking. She did the exact right thing to get him to acknowledge Jenny's existence. And again I also about cried in "Joruney's End" when the Doctor freezes when he hears Davros's voice and she was smart enough to realize he was in the middle of goddamn PSTD flashblack and needed to talked out of it.

I read a study once, long ago in college, which concluded there's actually more people than you'd think who haven't actively tried to hurt themselves who do try to hurt themselves just after beginning seeking treatment for mental disorder than you might logically think. The writer of the study seems to think that people would begin to a bit of hope and then be so terrified of loosing that bit of hope, it backfires. I look at end of season 4 and...yeah, I think of that study.