Hi Littleblue,
I can't give any advice on clicker training, but can sympathise with what you're going through.
Boris, my big fairy (shown below
) was from a rescue centre, we got him at 9 months, he had been getting fed on bread and milk and was a skinny runt of a dog with HUGE ears
and HUGE problems
He was very anxious and every time he was alone whether for 5 minutes or a couple of hours he would trash whatever was lying around - and I really mean trash, he destroyed (amongst other things) an iron, tumble dryer and a solid wood bookcase ! and we would ALWAYS get a mess, even if he'd just been - it was a nervous thing. I backed off from trying to train too hard to begin with and just let him settle - I'd say it took a good 15-18 months before he actually calmed down and he was younger than your girl so she may well take longer. Luckily he's okay on or off lead, but our other GSD wasn't, we tried a halti with a fair bit of success (up til the point when he figured out how to reverse out of it !) it might be worth a go just to get her to stop pulling. The other alternative I tried was a long lead (or horses lead reign) and just stand in one spot and let her run/walk in circles, gradually decrease the length of the lead until you are walking beside her round the circle. Once she gets used to that you can bring in changes of direction, stops etc (try having a bag of wee chunks of chicken or treats in your pocket on the same side as she walks, give her a reward each time she does as she's asked and eventually she'll get the idea)
It might take a while but IMHO once you get her sorted she'll be the most loyal and happy dog you've ever owned