I'm glad now that I quit working on this when I did. It's so easy to mess them up. I'll restart this training with a better plan pretty soon.
The multiple balls that are always there makes WAY more sense than removing it altogether and the down training with corrections as needed on a separate area than the send out makes perfect sense. I think the dog I saw that did terrible send outs and I was told that it was because mis-use of e-collar (not by the handler, but someone standing with me watching). Now I'm thinking if they'd needed that correction to down the dog but had never paired it with the send out, perhaps it would have been a different outcome? The dog was anticipating the send out with downs & corrections more than the fun of getting the toy. As you pointed out, they should go out with joy thinking of the reward at the end, but be totally obedient to drop down when asked.
Thanks for the input, it's all very helpful. I don't have help to hold the dog, but I'm already sending her from a good distance so I don't think I need that part ... how many paces is the full field distance?? I don't think distance will be a challenge, so when I start back on this I'll pace of the approximate distance. My other problem is her eagerness so I'm using a tab on the prong to keep her at heel. If I even begin to lean forward she'll take off. She leaks (barks or squeals) and wants to get ahead in anticipation of the send, when she knows the send is coming. I've tried heeling in circles or about turns to heel away from the ball, but seems to amp her up more.

Obviously, I need all the help I can get, but your info and that video have given me a better plan.