Any ideas for Daisy?

My rescue GSD Daisy had a nasty spat with a friend`s dog recently over a toy. I am now working with her on her posessiveness, but she is thoroughly enjoying the attention and being an absolute angel. We`ve done Leave, give, fetch, fetch after a Wait, teasing her with it and her not going for it, having her sit while another dog fetches it etc.
I`m starting to wonder if it was the toy that sparked it or if she was challenging the other bitch. She has ignored all other dogs since.
In any case, she is enjoying it (and so am I ) so any ideas for `control` games or excercises for us

Have you tried "find it"? It's Ollie's absolutely favourite game and you can play it anywhere.

Yes - also find it with another dog, and find it after the other dog has failed miserably I want control when she`s excited. Maybe I`ll start going to Agility again when I`ve had my high blood pressure treated.