IMHO, for someone unfamiliar with power tools this task is better approached with a jig saw. Freehand pattern routing on that scale doesn't seem like a good choice for a first woodworking project.
I suppose I agree with you, but with a little guidance, it could be an easy first time project. Provided that the tools were available and someone with a bit of experience.
If the jig saw is too cumbersome, one can always bring the plywood into the living room, set it between the sofa and china hutch, let the youngster carefully etch out her design with something simple, say like a hot glue gun, (great with glitter,..kids always like that),..then trim up the sides with something like a 36" Husqvarna,..it allows plenty of creative latitude just in case the outline is a bit off. Don't forget to cleanup with a nice shopvac or just use the leaf blower and everything will look good as new. ;^)