There's only three different themes actually, but there's a hojillian versions of her original theme from SS1. SS2 has a different song, as does SS3 (but as far as I remember those themes aren't used in any other games, maybe they are in the Nakoruru graphical adventure that was on the Dreamcast/PC).
Personally I dislike the first two (I HATE her SS2 theme), but I really enjoy her SSIII theme quite a bit.
The beginning of the original theme in the SS64 AST is pretty classy though, nice mix. That cd kicks ass in general