
As another non driver who fostered some rescues who had never been socialised I found the best bet with these girls had been a half check collar and a body harness, the rigid kind not the non pull ones. the ones I favour are the ones that have two D rings above the fastening, so if the clasp should give the harness cannot come apart as the two rings the lead is attached to keep it together. Canac and Hi craft both make this kind.
I found by having both the collar and the harness it gave me more control, and the harness acted as reassurance. I did find for safety both were needed in case the dog panicked, as in that situation dogs can get out of harnesses and collars.
I started with taking them into my front garden and just sitting there. Not making a fuss of them but just sitting chatting inanely and whenever they seemed to relax just a quick pat and jolly hockey sticks voice.
We progressed to walking (well I walked they didn't at first) just to the street corner and back (*I am the fifth house from the corner).
After I had got them walking, any time they startled (a lot), I would stop for a few seconds just so they could see what it was, and then very brightly say come along now, and move off briskly.
I went a lot to our local shopping centre (20 minutes walk away) after I had got them walking in traffic OK, started with least busy roads in daylight, then eventually to darkness with headlamps etc.
At the shopping centre I would sit on the benches and just chill. People would come up to enquire about the dogs, and depending on how far they had come would let them great or explain the situation, and not allow them to touch or make eye contact with the dog, but because I was speaking to the people the dogs got to realise they were no threat and we could progress to greater contact.
You need to start getting her used to all these things at first from a distance where she is just mildly stressed, and build up. A terrified dog cannot learn anything.
I would say never take her out with the pup until she is 150%. Shepherds are naturally protective and sensitive dogs, and you could end up with him trying to protect his Friend, or even share her fears.