Hello,
It seems like the dog is confused of what you are trying to show her. She is not sure what she needs to do.
The reason: she is still a young pup, and is having fun.
When she gets a little older, she will need to be "force fetched". At this point, she is retrieving only when she wants to. She has not learned and fully undertood that she Must retrieve on command. This is a process that needs to be taught properly in the force fetching program.
I would not use the command "Back" for marks. This is normally used for a bird that is already down, and then the command "Back" is used as a blind retrieve only. I would only use "Fetch" for now on happy bumper throws and short marks. Eventually she will be released for the mark using her name command.
Like I mentioned before, she needs to be taught all retrieving drills before you can make her understand the command to fetch. Skipping steps in retriever training and hurrying the plans for the pup will only cause you grief in the future.
If you are planning to run her in hunt and field trials, and as your hunting companion, you could get into situations which she will not respond to your commands when needed, and this will only cause confusion for her and disapointment for you.
Please get in touch with me if you require further help.
Regards,
Kristine Dunham
HighlandPeak Kennels