This seems to be a bit of an old topic, but oh well, here goes anyway. I just listened the song today, and it sure sounds like her. Checked the lyrics too, and as a whole it goes something like this:
"There was a little drawing of a heart next to that,
followed by an exclaimation mark.
The back of his was covered in stuff stuff like:
Brandon is not a very nice guy, but Alex is sooo nice.
And that had the exclaimation thing too.
It was just silly crap that hit the spot. And he let himself be drawn in."
If someone remembers a scene that goes like that in As If, please let me know. This kinda bothers me.
"God must have a huge beep sombrero up in heaven!"

on the album spoken text is credited to Juanita.

Just had a listen and totally agree - she has a very distinctive voice and it definitely like her.