Aw, you are afraid your doggie will have a hard swim in Westwater......My deepest sympathy for your concerns.
Damn, it's a dog. If it drowns, have it for dinner. Well, I guess, my family would also be bummed if I only brought home a small rug after taking our wonderful 2 year old golden on a river trip.
Seriously, though. Here are my experiences. My golden swims in rapids often. She usually has a life vest on. She has learned a type of dog paddle that pushes her nose above water. With that and the life vest she can keep her nose 18" above the water--above most waves. She does pretty well through the rapids. I've seen her submerged by an eddy and she doesn't cough when she comes up.
I once took her through the Deckers chutes section and she got caught in a very small hole in the main chute. She was recirculated for about 20 seconds and then spit out. No problem. She did fine. So if your dog is used to a river and if you give her a life vest, she should be fine.
I guess if the dog goes on a long swim through big waves when there is high water in Westwater, you may have a problem. You can't rescue her with a kayak very easily.
My dog life vest and most others have a handle on top. It's very easy to haul the pooch out of the water. You should be able to clip on a safety clip to the handle to pull her out of the current with a kayak.
The bigger problem I have is that she gets cold. I posted the problem on the buzz, got great answers, and was pointed to a neat dog wet suite. It also provides buoyancy.
As for more standard first aid, they sell doggie first aid kits at Petsmart and probably REI. But, all you really need is antiseptic, gauss, and tape.