Will she pick up a freebie with any frequency? If so you might want to switch to pressure on refusals only and let her have some success, or every few retrieves instead of every single repetition. Usually by the time I get to collar conditioning a behavior they will do it pretty reliably without pressure. Collar fetch need not be any different, right?
last nights session went a lot better with no struggles between dog and handler. I switched from holding her with my hand underneath her collar, I put a leash on her and stood right beside of her, put bumper on the ground about 5 feet in front and worked it from there. I took Darrins advice and only nicked on maybe 1/4 of the fetch commands. I bumped up the intensity on a few to make sure where we were, got a whine but she pushed through to make the pickup then the next few would get a really quick response with no stim.