Hi Tristan,
I have absolutely zero experience with training dogs, but I'm sure that I read on this forum somewhere that in order for a toy to be a motivating factor that it needed to be owned by you as the Alpha. As in, you only bring it out at certain times and then put it away as well so she has no access to it in the meantime. I just noticed that somewhere you wrote that Flossie would bring you a toy at certain times. Maybe if you had a special toy that she loves but is only used in training?
As I said, absolutely no experience
Good Luck with your training.
Sunsoar