(By the way, this happens a lot. We let under-10 kids fiddle around with our kayaks and they are ALWAYS fascinated. As I've mentioned here before, I think there's a market for a little kayak specifically targeted at this age group. If we can capture their imagination then, they'll turn into full-sized boat buyers in a couple of years.)
I suggested putting her into an inflatable so she could try the river, and while she was interested she immediately said "But I want one of those solid ones, not some blow-up toy." Smart girl!
So... any recommendations? The Dynamo is too large. I've heard of something called the "Pinball" but don't know anything about it. She's still a child, so she doesn't have any hips and thus it will need a narrow seat (or a LOT of minicell). A used boat (to keep the price under control) would be a big help for her parents, too.