BECAUSE SHE IS ALLERGIC TO HER OWN GOD DAMN TEETH!!
okay, technically that isn't true. apparently she has lymphocytic-plasmacytic gingivitis stomatitis (LPGS), which means she is allergic to her own plaque.
since you can't really have teeth without plaque, it's basically the same thing in my eyes.
at least now we know why she smells so bad.