So sorry to hear about this. It's inexcusable for people to be so rude and the JR owner should not be allowed to let her dog behave like that especially as she knows the reaction that will happen.
First a question: has Freya ever met the JR while she's off the lead? I'm asking because when Jonny and Jess met an aggressive GSD one day while all three were off lead, Jonny ran for the hills, even though the GSD was actually attacking Jess (he'd had a scary encounter with a GSD before and was and still is terrified of them). Jess, who was a very timid wee cocker, rolled over onto her back immediately and after a very scary (for me) moment, the GS lost interest and his owner managed to drag him away. Jess was fortunately unhurt and not particularly upset. Thereafter, with a few exceptions, she would avoid eye contact with other dogs we met and slink along the ditch or undergrowth and keep a low profile. Funny wee thing!
The other thing is, I used to have a JR long ago who could be aggressive to big dogs such as GSDs. I was very careful to watch her body language when we were out and about if another dog approached and if I saw the hackles go up, I knew to get her on the lead. However, if she approached with tail lowered and her body in a 'comma' shape, I knew she had friendly intentions.
I don't know if any of this is helpful, but I can so understand how you feel with Freya. Other dogs will be dogs, but owners can be a nightmare! (I once was clasped amorously round the waist by an oversexed collie who refused to let go while the owner walked by either oblivious or deliberately not looking!)
Di