If you want to do AKC obedience, agility, rally, etc, then you can get a PAL number (probably). If the dog looks like a GSD, then look up the requirements for PAL on the akc.org website and fill out an application with the required documentation.
If you do not think she will pass for purebred, you can go with canine partners and then you can participate in AKC shows that allow mixed breed dogs and earn titles through the AKC.
I am not sure of the requirments for fly ball, who sanctions those trials.
A good goal for a new dog is to start with a CGC, (Canine Good Citizen). This is just some basic commands, walking well on lead, not reacting badly to dogs and other distractions, and the killer for some, supervised separation. Once the dog is through the CGC, then work toward a title in whichever venue you like best.
Heidi Ho, Odie
Joy-Joy, Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.