[user104658]

Originally Posted by Oliver_W

To be fair, I think that was meant to be her "endgame arc" - she was running around, pretending to be the Doctor, and that's what got her killed.

Spot on IMO Oliver - she learned from and idolised the Doctor and forgot (perhaps both of them forgot?) that the Doctor regularly gets him/herself very much killed and is only able to be The Doctor because of being (essentially) immortal, or at least close to it.

Though on that note, I think it was a narrative error to have her go off adventuring in her own TARDIS as her grand finale. Story arc wise, given the above, she should have died.