> why mum is guarding stuff like this
To show her daughter she is boss.
I would remove any treat that aren't being actually chewed and not allow her to do this.
I have had individuals so this usually with their food to show the others they can, I show then they cant if your going to guard it then it goes.
Your quite right the real issue is the balance of power between the two (the pups is approachign maturity) which is being rocked due to the hormones with the season/phantom.
I would step up discipline for both, sort of knock their heads together so they don't have time to be worrying about who is top bitch as they can see you are, and are too busy worrying about what your expectations/demands are.