I would suggest reading through the posts on the Puppy Place here. There are several aggravating stages they go through just as with other breeds. As far as your older dog, the time may come when you have to separate the pup from her as she will not be able to handle the activity a puppy creates. Be prepared to gate, crate, and rotate if that becomes an issue. Other than that, be sure to train early and often and never stop training. I personally believe that German Shepherds are the most intelligent, beautiful, willing to work for you breed there is, but I may be a bit prejudiced! LOL! Good luck on making your choice.
Snake Vom Eselspfad RN CGC (AKA Raina) 3/5/08
Pyrate CGC 4/1/03-5/16/12 RIP
Too many to list waiting at the bridge but remembering them all