Time and again, Ness and friends save Pop Star from potential threats that are too much for Kirby and his thugs to handle alone. Charlotte, being the impressionable lad, sees someone who has just as much capability as she does (as far as she can tell) using it for the greater good, and of course is going to want to be like Ness. It's like Tails wanting to be like Sonic, at least in the older games. And let's not forget her little crush on him, which would also have a lot to do with cosplay.
PK LOVE, indeed.