I've got a couple of ideas too; you don't have to take them on board, but you did ask. XD
Multicoloured hair. In other words, hair of unnatural colours, like pink, blue and green. Plus streaks and fringes (bangs) to add to the current hair pieces.
Hair stuff. Ribbons, hair bands, ponytails, plaits.
Chunky heels. Like
this. Also, platform boots would be great.
Animal print. Cow print, leopard print, zebra print, dalmation print. This might be difficult, but would look great. Also some more patterns; I love the patterned skirts!
Jewelry. Nothing too complex, just a few extras to complete the doll, like necklaces, bracelets, earrings.
I also agree with Kitty's suggestions. XD