Well, in mens, a size 9-10 requires around 25cm at the waist so she's good.
Remember, the board is actually a little wider at the binding insert points where her boots will lie. Her angles will also affect this. So even if the board was a little narrow (which that particular one isn't), a ducked stance would resolve the issue.
She's good to go with that board.
For Michigan riding, easy in/out bindings are awesome. I have the 2010 Flow NXT-FSE and looooove them. I bought it mainly for the comfort though. Most comfy pair of bindings EVA! But if you like the response of traditional straps, the Cinches are a good idea. You should also consider the K2 Autos. K2 Auto Ever would be nice on that Magic of yours.