Gets left behind at the end of Time-Flight but rejoins the Doctor in the next story Arc of Infinity. Damn. Actually she's alright in a few stories like Kindaif you get past the bizarre not-very-Australian accent and whining.
At the end of Resurrection of the Daleks she's so upset by all the arse-melting, vagrant-raping, rectum-probing, Dalek-raping action and insanely high body count that she can't handle it anymore. She seems genuinely traumatized and shocked by what she's been through. "It's stopped being fun," she says, "I'm sick of it." And then she runs off, while the Doctor begs her not to leave like this.
And of course The Doctor fucks off in the TARDIS just as she comes running back. Poetry.