14 wks and she'll chase a bumper, let her chase the bumper, don't worry about the return yet, let her chase those bumpers as far as she will chase them. Work on here etc. without the bumpers , soon it'll all come together. Chasing is marking, marking is good, going out on her own is good. Retrieve will come later, you can start with hallway retrieves, to get her to bring it back, but you might want to use something softer and lighter than a bumper. Plastic bumpers can be heavy for a pup, they can also hurt their teeth, you don't want a bumper to be associated with painful mouth. If all she's doing is running to the bumper and not picking it up, your good, now when they start picking it up and running off (15-16 weeks) a rope is your friend

, I'd get HERE trained and enforced before that happens

.