Maxi-Scooters like the SilverWing, Burgman, Majestic, are perfectly capable for Interstate duty. Dial up some You-Tube videos of the Burgman 650 and you'll see some striking performance. We have a Burgman 400 and my wife a capable experienced rider, has no problem staying with me on the FJR on highway outings. They mostly have 14,15 and now 16" front wheels. The Honda Interceptor had 16s.
As to the accident, tank slappers can be brutal and nearly instantaneous. They'll throw you down on the ground so hard and so fast...
In that circumstance, she likely hit a hole, bottomed out the suspension inducing the tank slapper. There is no recovery. having been the victim of same on my Hawk, with full size wheels.
Correct me if I'm wrong Chris, but that stretch of I70 is a 55mph limit, tho traffic pushes hard. If I were on our Burgman thru there, as much as I am comfortable on it, I'd keep to the right and keep the speed down, and stay very defensive, not aggressive.