Omg, I love this anime so much! Like, definitely top ten. And I think Shiro is one of the main reasons I loved it so much. And I don't ship her with Sora (that's gross), but I do think it's cute when she makes jokes about it; it definitely gives the show a lot of comedy which I like.

Now, I have decided that Shiro is 50% Kuudere, and 50% Tsundere for the following reasons:

-She is shy and doesn't talk to most people (excluding Sora)
-She has an adorable blushy face
-She doesn't seem to be affected by most things (excluding being away from Sora)
-She does (although they're jokes) make jokes about being in love with Sora.

Those things might not seem to exactly fit the categories I've chosen, and maybe they don't, but, here's an example;

~~~~Example~~~~

Sora: Hey, Steph, come over here.

Stephanie: (Walks over to him) W-what is it, Sora? (Blushes)

Sora: Oh, nothing. (Sly grin) I just thought you wanted to see the face of your lover! (Reaches to kiss Stephanie)

Shiro: (Holds on to Sora's sleeve preventing him from moving) Baka Ni.. (She shortens Onii Chan, to Ni) I thought you said the only one you needed was Shiro... (Blushes)

~~~~End of Example~~~~

Isn't Shiro a kawaii little Tsundere-Kuudere cross?! I just.. I just love her so much.. Sora is a lucky man..