I would do the basics, like everyone else said. I'd also choose a few fabrics...not stash building, per say, just something that is just hers, kwim? Like a charm pack or a few co-ordinating FQ's. Nothing big...you could even pull from your own stash and cut some for her.

Don't forget to put a seam ripper in!!! Several spools of thread. I love to see the young kids interested in getting started in sewing.

Make a really cute pincushion with some pins with fun tops. You've got lots of ideas here...My granddaughter loves to collect fabric and has her own box at my house. You won't have to spend a lot of money to get a fun basket for her.

when my granddaughter asked for a sewing machine - i gave her a quilt box with all the things mentioned already - but i think at 8 yrs old some precut blocks would be a good thing. that way she is ready to start on her own quilt immediately.

Maybe toss in some fusible web, applique can be a fun beginner project too :D:D:D
A few spools of brightly colored thread?

I'd get her a pattern book geared towards teens or make her a binder full of ones you found online with the patterns in plastic sheet protector sleeves.

I'd get her the longer pins, a magnetic pin cushion (I looove those things!) and maybe a tool organizer. You could either make or buy one of those.

You could also start her off with good habits and include a pair of glasses - either with no change in vision or the reading types to protect her eyes.

There are just so many notions out there that if I were in the same position, I'd go overboard!
It also really all depends on what kind of sewing she wants to do.

I hope you are getting her a "real" sewing machine that she can grow into.

I would have said seam ripper. Mine is connected to me.

So many great suggestions, I need to look up a pattern for a pin cushion and tool organizer.
Bearisgray, yes she is getting a real sewing machine. It will be new to her but it is actually an older Singer, that I found on Craigslist and took it in for a checkup.

How about a used machine, either at a yard sale, thrift store or even your local sewing machine shop. The last machine I got at the local Humane Society store, is a 70's Kenmore, works great and the best thing is, it cost me $10.00.