Hi Michael. As an FYI, I sent my motor parts to Jack Moore. His username is LT80 on just about all ATV forums. I'm not sure who else builds these motors, but for what it's worth, my LT80 absolutely flies with his mods. He walked me through important details putting it back together too like new torque specs for the head, how much to advance the timing, and gave me lots of other tricks I could do on my own also. He was a really nice guy on the phone too, which is something I haven't always experienced with some other builders.
One word of caution though! I got nearly all of his engine goodies other than a lightened flywheel. It was almost more than my son could handle until we got used to it. With stock length wheelbase, it's very difficult to take off withouth the front wheels coming off the ground. Some of the biggest mods he makes are to the clutches, so the motor is allowed to rev a lot before it starts moving, and it hits like a freight train when it does start moving. Your daughter will have to learn to feather the gas a little if she's just crusing around. Or, you may talk to Jack about getting SOME of his mods, but not a full on race motor if you don't want a pure race quad. But, I guarantee you he can give you more power than you need from you 80 engine.
As Mitch said, suspension is very important with this bike too, maybe more so than the motor. The stock stuff is marginally better than having no suspension at all, especially with a fast motor.
You'll want to widen the bike for sure and get better boingers. I would look for a used set of Works if you're not wanting to spend too much. But if you're willing to buy new, look at Elkas. However, they don't sell a lot of shocks for the 80 so they have to be made to order. This can take awhile. (I waited for a couple of months.)
Good luck!