So this is the little Pan from the final chapters of the manga. Let's say #18 opted to take part of the 28th Budokai and got to face Pan. Who'd win this?
Pan's strength at this point is quite vague with the only indication being Goku saying she'd still get far in a tournament where she had a good chance of getting pit against one of her allies. The only source we can go to solidly place her is the anime showing her as stronger than Base Goten, and Goku's statement suggesting Goten wouldn't be so stressed about fighting Boo if he hadn't slacked off would suggest he's at least a fair bit stronger than during the Boo Arc. All that said, Pan wins, whether it be with difficulty or easily.