You need to start obedience training now - yes, now. Dobermans are very, very smart, and you need to train them when they are young and keep at it - she will be a large strong doggie when full grown, so set the precedent now, when you still have the upper hand. But also keep a spray bottle of water handy so you can spritz her just to startle her into stopping when she start nipping at the older dogs. Dogs aren't born knowing what "No" means, you need to teach her, and if the older dogs won't play, or correct her, you need to! Also have plenty of chew toys handy to substitute.