My GSD always herded my kids. She always circled them and tried to keep them in a nice little flock, and got very upset when they separated. GSDs do like to keep the family together.
Yes, she needs to be trained now, before she gets any bigger. Definitely before the teenage hormones kick in.
Training classes are a must as she needs to learn to behave.
A couple of things might help - find out about positive training, especially using play. I find toys a wonderful aid - better than treats. And see if you can find someone with polite dogs for her to walk with and learn manners from? Dogs need to interact with their own species, and need to learn the language.

Hi. We do a little training with her everyday. Heel work with me and general day to day sit, down, stay etc. Absoultely perfect at these.

You say to train her off the lead for 5 minutes or so but my problem with this is that she will run off especially if there is another dog. She will come back if i let her off in a secluded area its just when something of more interest comes along.

I have a large playing field next to me which i would love to walk/run around on but again as soon as we are on that field she goes bananas and tries to pull/bark towards the other dogs.

First steps to take.... any suggestions???

If you're sure she has mastered sit, down, stay, wait, and the heel walking take the heel walking to a place with a low level distraction. How about the field at one of the quieter times? Keep the distraction at a distance she wont react to, if she reacts you've gone to far and need to take a step back.
could you not practice some offlead work in the house or garden?

Also get yourself a long line and work on some recall training. Reward her each time she comes back. Never scold or punish her for coming back to you - even if shes taken ages. At first if she doesnt come when called use the longline to gently pull & release to reel her back in.
You need to make yourself more exciting than the distraction - this way she will want to come to you.