Vanessa said that when she was little she used to imagine that there was a ghost girl who lived in her closet and that's where the inspiration for She Floats comes from. She explains it before one of the live versions of the song I have, but I haven't heard it in a while. If I've got it a little wrong, someone feel free to correct me. I think that is pretty much the gist of what she said though.
But what Vanessa is actually writing about doesn't mean jack shit. It's interesting trivia, but what really matters is how each individual decides to interpret it on there own.
Interpreting the song as suicide or drugs or whatever...it's all good.
Even though I know Vanessa's actual inspiration for that song now, I still interpret the song being about a girl who is coming of age and is kind of lost and feels detached from the world and she is just waiting to find her place. That has more meaning and relatability for me personally and that's how I'll always hear it.