Hi Elsie -
You asked if you should go back to clicker training - what kind of training have you been doing since the clicker training?
I'd recommend a number of different things, and you can pick and choose what you think may work for your particular dog.
One, you may want to have a health check done to make sure that she isn't uncomfortable in some way. Is there a sore in her mouth that makes her not want to pick up the dumbbell? Does her back hurt? While I know you said she does nicely in practice, a lot of times dogs will do well in situations where they know you can enforce commands but give in to the pain when they know they can get away with it. It doesn't hurt to have her checked out, anyhow.
Two, using the concepts of clicker training may very well perk her up. One of the difficult things about positive training is to make the time between rewards long enough to work in a competition ring. When we reinforce relatively frequently in practice and then are unable to do the same in trials, the dogs quickly figure that out. For some dogs it doesn't matter. For others, it means they quit working. So you may have to gradually extend the amount of time between rewards so that she has the stamina to perform all the exercises in a trial before getting that treat or toy. Another thing I would do is to practice random reinforcements. Go into your training area before you take the dog in, and put several stashes of treats or toys around the area. Then bring your dog in and at random times mark behaviors and run to one of the various stashes. You want your dog to think she never knows when or where a treat will appear!
Three, if you've started using more corrections as "proofing" then I'd discontinue that. Some dogs are just so sensitive to corrections that it ends up shutting them down. I'd stop trialing as you work through this. Keep things upbeat and happy, and try to always stop your practice before she shows any signs of being tired or uninterested. Try putting her in her crate and letting her watch while you work other dogs. Sometimes the competition helps build excitement.
I've found that every dog is a bit different in what they can handle as far as warm-ups go, too. I'm still figuring out what works best for my young chow. Last trial I brought her in and had her in her crate for a few hours beforehand, took her out to get a feel for the place for awhile, and found that too much waiting tended to de-motivate her. Next time I'll do less of that to see how she does. There's just no way we can imitate the feel of a dog show. While I wouldn't say I get very nervous anymore (put my first obedience title on a dog in 1990), I still have a level of excitement even in me that I don't get in practice or even at fun matches. When you've paid all that money for entry fees and traveled to the show you just plain have a lot invested and you WANT your dog to qualify! So there is a change in us and then all the strange dogs and the strange place all works on our dogs to create a level of anxiety in them.
Good luck, and I hope things work out!
Melanie and the gang in Alaska