RRR
If she was washed out by a professional using the "standard" Rex Carr based e-collar system then it seems unlikely that more of the same is going to get you anywhere, at least in the short or mid term.
Given that you have many other dogs and a small breeding business to run, you need to think about this one. Just what are your hopes and aims with her? Re-sale as a trained dog, keep her as a brood bitch, develop her as a shooting companion? My experience in remediation training suggests that in her case their isn't likely to be any fix that is quick or easy. The brute fact is that there may not even be a fix.
I'm not going to lay out any rules and regulations as to how you might proceed, but I'll tell you what I would do in similar circumstances.
1) Figure out just how much time and effort this dog is worth to me as opposed to letting her go as a pet. Am I better off making a small loss now as opposed to a larger one in six months?
2) If I decide to persist, I'll set a time limit. The heads and brick walls rule will apply!
3) All pressure based training is going to be cut out and discarded; I need to get this dog on my side, and liking me. I also need to get to like her, which isn't always as easy as it sounds.
4) First training step .... Six weeks of R and R down by Ray Roberts Lake shore, just playing and swimming and messing about., preferably with the other dogs if it won't interfere with their training profile.
5) Taking Dennis's point, I need to find out just what I've got, I need to determine this dogs attitude to training, any sort of training. So I'll teach her a few daft tricks that if they don't work out won't affect anything more serious; "shake hands", "salute the flag", "play dead". And then (really crafty) fetch the newspaper; it ain't a bird, it ain't a bumper, and there's no pressure, and nothing went bang. If you have only ever used coercive training methods you'll need to put another hat on and learn something else.
6) If I've done OK up to this point, I'd to take her into a rabbit pen and see what happens; judge her instincts on something she hasn't seen before but is very attractive.
7) If she wanted the rabbit or even better, put in a good chase, I'd shoot one and sit down to wait. And that would be the tipping point, if she made an attempt at a retrieve or showed interest I'd know I've got something to work with. If not, it's a pet placement with no breeding from her. Even if it didn't work out I have learnt something along the way.
Like I said it's not a formula for you to slavishly follow but it's a similar approach to what I've done in the past; the basic idea is to get the dog and me relaxed with each other and then do an assessment of retrieving potential in a stress free environment. That's the best I can do from 6,000 miles away, if it suits you then I'm pleased, if it doesn't my wrists remain unslashed!
Anyway, best of luck,
Eug