Please help me in making my first Tokidoki purchase for my niece!

If she'll be using it for school, then get the campeggio. I remember being 12 and having to bring 2 big binders and a ton of textbooks, so the stellina and probably scuola would be way too small for her.
 
Ok I second that, go with Campeggio. Now upon remembering my 7th grade days, a small bag for school won't do her any good as she'll probably need to bring at least several notebooks and binders, not to mention possibly textbooks now and then, and all the little pens/pencils/accessories she might choose to carry.

I do have a Scuola but I tried putting a 1.5" binder in the main compartment and it wasn't happy vertically (but there was still room in there for smaller books or notebooks). The Scuola's front pocket and mesh pockets did come in handy, though....the Campeggio comes close to that with its two front flap pockets and the inner pockets/zipped pockets.
 
I think Campeggio might be a little huge for a 12 year-old. I found it a little huge for myself. I'd say Scuola or maybe even Buon Viaggio might be easier to carry and less bulky for her. Then again, someone else said Scuola is a bit small, and I've never seen one of those in person. Buon Viaggios are pretty big, but I found them to be less awkward than the Campeggio. (And it felt less huge to me.) :shrugs: