Are you saying that the dropout width on a 7-speed is narrower than an 8-speed (I thought both are 126mm) or that only the freehub body is narrower on a 7-speed hub than on an 8-speed hub?

If I go the 9-speed route with one less cog, how do I keep a 9-speed shifter from shifting the chain off? Will the RD limit stops stop shifting at the 8th cog?

Also, I read nothing good about Sora, so probably do not want to go that route.

Here's a pic. Ain't she sweet. Just the ticket for my 5'1" tall daughter.

Thanks.