a typical boxer pup,
keep going to the training classes she will get there in the end.
try putting a line on her basically a long rope with a clip on the end make sure you put some knots in it, then if she looks like she is going to run off stand on the rope call her back give a treat.
it will take time with her, boxers seem to not have many brains when it comes to the fun, they love to go see everyone and to play untill they are older they may calm down some.