
My guess is that you probably didn't start early enough ;) Not criticising you and it's a common problem. All puppies need to be groomed from day 1. How frequently do you groom? You should really be doing 10/15 minute sessions daily to get her used to it, IME, you can never start early or frequently enough.
I now have two Briards and a Briards coat is very hard work, think Old English, Beardie etc. My pup in particular is now starting the difficult, knotty coat stage and if I put up with any nonsense then her coat would be dreadful and as a last resort, need to be shaved

But I have also had Shepherds for many years and my last one was very long and thick coated.
Now, knowing how strong willed and determined Shepherds can be, you can't afford to take any nonsense. She is doing this because she's been allowed to do it. Yes, treat by all means, but only when she is calm and accepting of you grooming. If you stop grooming when she's being difficult she will associate her behaviour with you stopping and then she is rewarded for misbehaving...........hope I haven't lost you so far with my long winded description :D
Don't worry about it taking 2 to groom to start with, as long as you achieve the desired result, eventually she should grow out of it as long as you are regular and consistent.
I bet she looks gorgeous afterwards :)
Good Luck, :)