I click and treat her when we are walking past other dogs on lead. This has worked well and she no longer lunges at other dogs.
If she is focused on off lead playing dogs she will spit the treat out.
She doesn't get to play with every dog she meets. I assess the situation first before letting her off. But once she is playing if another dog comes along then I can't stop her going to that dog so at that time she gets to play with every dog that comes along. I used to worry about her going off with another dog but she now always comes back to the dog we are with.
I have never needed to use a line before so it has been a big learning experience. For months I used the line to give her a bit of freedom whilst keeping her away from other dogs. But I have since been shown that I can leave it on her while she plays with other dogs. I put it on her harness as soon as we get to the field and often keep hold of it if I need to stop her running off. Sometimes I call her back and let her go to a dog to play. Sometimes I let go of the line and let her sniff or play with a tuggy. Where we are alters her reaction to toys. Certain places she doesn't show much interest but other places she gets much more excited I really don't know why. Perhaps the quality of the smells.
As for her gsd instinct as I say I doubt if she has got any. She is certainly not like any other gsd I know or have known! Unless I set up a formal training session I don't really have anyone to help.

Fab she has responded well to the clicker when out...I have yet to try this with Tango but that could be a job for tomorrow now you've said that

Out of interest, if she is focused on an offlead dog...do you click her and then she is getting the treat she spits out, or do you just give her a treat? Do you always use the same treats? Do you have some really high value ones and some boring ones? How do you get her attention? Do you say her name a lot? Does she get offlead to the dogs she shakes when she sees...or the ones she is totally focused on? Could you get her to sit, or is it beoynd that?

It's a class for reactive dogs (not aggressive) so there are low barriers between dogs when working and the emphasis is on getting the dogs attention when working near other dogs. Lying on the mat and relaxing is part of the class. When she moves away I am just told to relax myself as much as I can in order for her to relax too. She is getting better. She used to sit there staring intensely at me willing me to treat her so I can't reward her with treats for relaxing.
At home she is ok about being stroked within reason. She is not a cuddle bug!

I would like to try that. It would be fantastic if I could get her to retrieve.

Is this something you would recommend doing when another dogs gets her interest?

Bless her! She obviously sees other dogs as thwe greatest reward ever...so needs to associate them with being less of a reward than something else...which is obviously the thing you are looking for, that something else.

Does she have a good sit wait?
Could you sit and wait her on a longline (holding the end incase she spots another dog) then walk behind her and put a toy somewhere and get her to 'find it' then huge play session treat and reward...lots of excitment and praise? ONLY allow her that toy when you do that...at NO other point ever.

I wish I knew who made the training rope/pocket thing...I am not at agility again til Tuesday but I will try to remember to ask the trainers as it is a fab toy, we are going to get one ourselves (but keep it quiet..it's for Christmas )

Gosh I'm not sure I can remember exactly and because it varies depending on the situation but here goes...
I think what I would normally do would be to call her back, on her line and reward her with a click and a treat. On a lead the treats are just kibble. Off lead I mostly use chicken, roast beef, sausages. When I call her back I use 'Tala come'. Other than that I don't think I use her name a lot, I seem to remember being told not to when training. We also practise an exercise from the class which is Look when another dog comes into sight and as soon as she looks click and treat. This is to allow her to do what she wants (look at the dog) and then focus on me. I can always get her to sit but not to look at me and not to walk calmly towards a dog she knows. Well perhaps I could but it might take a few hours to walk a few yards. And yes she gets to play with the dogs she knows although I have in the past kept her away from that particular field. In the morning we sometimes walk with a few dogs and if we have done that recently just getting her to walk to the meeting place without pulling takes considerable time. But once we are stationary she will sit calmly and with these particular dogs she doesn't shake. I think the dog that excites her most is the first dog she ever ran off lead with.

did you train the whistle with a long line?

i might have missed it, but did you go thru the long line stage at all?

I won't breathe a word I will certainly try getting her to search for a toy. I have taught her to 'find' food which I scatter on the ground. But in order to do that I will have to take her somewhere new because she will be less receptive when walking where we have been recently due to expecting to play with dogs. This is what I meant when I said the more she plays with dogs the more she gets excited about playing with them. On the other hand I don't want to go back to keeping her away totally.
I have tried to make a toy special to her in the past with limited success.

Sorry I didn't mention it but yes I have used a whistle and line and she is very responsive to it on a line even with another dog close. But unfortunately it didn't transfer to offline when playing.

We've always treated ours when they come near - right from tiny pups. Although it might not sound like it the little exercise I described really is very different. I don't know if I explained it clearly enough but I really do urge you to give it a try. Ignoring the dog is an important aspect of it. The trainer based it upon theories in the book "When Pigs Fly" - I think you'd get loads of excellent ideas from that book.

As for lure coursing/racing - if you're ever in Scotland look me up and I'll put you in touch with the places we've used or else give you a go on our lure!!! But to find something in your area ask around at whippet or greyhound racing clubs. They'll often open their doors to other breeds. My guess is that a non-hound/terrier might do better if they start out on short, straight race tracks - so whippet racing might be best. A lot of the other breeds loose sight of the lure on a long, iratic course. Check out the 'other sports' section on here as I know others do these sports too.

What about flyball. For some reason that tapped into my girl's chasing obsession quite well. To teach her to play with a ball (she had ZERO interest) we cut a slit in a tennis ball and popped a treat in. She had to fetch the ball to us so we could fish the treat out for her. She's gone from being totally disinterested to pretty ball obsessed. Enough to keep her from running off. But let your attention slip for a moment and she could be out of sight in an instant.

One slight word of warning - ours went from adoring all dogs to being totally obsessed with me and our games. And part and parcel of that was a tendency to see off any other dog that came near us!!!!!

But it's all very modal. If I engage her I have no problem keeping her close. But zero chance of a casual stroll along the beach with the dog at my side. And zero chance of her running and playing normally. She's either a distant dot on the horizon or pestering me obsessively!!!!

That sounds a good idea. What stops the dog lying down and chewing the ball to get the treat out