She's gone all manic depressive. Most sufferers have distinct manic, then depressive episodes. Stacey seems to have both of them, intermittently, on & off during the course of a day.
I think she's been sleeping rough under the viaduct.
She mentioned something about meeting a guy who was going to teach her how to be a DJ.
Then her mum asked where all her belongings were and the way she asked Stacey where her underwear was, indicated to me, that perhaps she wasn't wearing any.
I can't understand why her mum didn't take her to see the Doctor, she's obviously aware Stace has mental problems
I think maybe she's caught up with Sean and he's gone a bit loony too? Maybe some didgy mates of his had their way with her?
It would just make sense as he keeps popping up in conversation/photos in scenes with Roxy, so it would fit in qute well! that he's due to come back in the storyline?