ReBoot

^
I'm liking this idea even more. A factory-produced pop-star. Well said, as well.

Thing is, what use would Serenity have for such a sprite?

Oh, and her appearance - much more clean-cut when she's on Serenity's side, wouldn't you say? It'd hardly make sense for Uncle Bill, while creating this glistening, white, pristine city, brings in a colorful character such as this - I can imagine her starting off looking much more clean, wearing white, etc etc.

Bread and Circuses. Synth would be part of the Circus -- keep the citizenry entertained (distracted) and they'll let other things slide.

See more here:
http://en.wikipedia.org/wiki/Bread_and_Circuses
and here:
http://en.wikipedia.org/wiki/Japanese_idol
(You may be familiar with its Romanized name: idoru)

Strangely enough, rek, I already know what you're talking about. Another good point.

Thing is, about her appearance - clean and pristine at first, but becoming all grungy later while joining up with the Rebooters?

I can't decide. Either she should be clean and glossy because that's how things are, or she should be in Technicolor® because she's a celebrity, a fantasy... 'how can you say Serenity's restrictive, just look at how Synth dresses!'

^
Haha - That's a good point. Either way would work, I think.

You should start a new blog just for discussing Synth, or post your ideas for her to the Writer's FAQ blog.