Does anyone have tips on giving a fidgety, uncooperative dog an insulin injection?

Not sure how big your doggy client is, but could you distract her with a treat placed on the floor, then quickly give the insulin shot in the scruff of the neck while she's after the treat? I give my own dog shots twice a day, and give client dogs shots. I ask the owners in detail about their own process for giving shots so I can follow the same routine as much as possible. Unfortunately a biter may need to be muzzled for your own protection in order to administer a shot. A higher number gauge needle (the higher the gauge, the thinner the needle) might help it be more comfortable for the dog, if the owner agrees. Good luck, I know shots can be a challenge. Be confident and do the shot quickly while the dog is distracted, if possible.

If you can, check out Dr Sophia Yin's info on low-stress handling.

Here's a link for a lot of the promo videos: https://www.youtube.com/watch?v=vBqng...

The second clip on the playlist shows the hold that will likely be most useful for your purposes. A second person is pretty necessary for both proper restraint and injection. If the dog won't hold still on her own it's very hard to administer the shot, and there's the chance of breaking the needle tip off under her skin if she moves suddenly. If you don't have a second person, I'd suggest a blob of peanut butter to keep her occupied while you quickly grab her scruff and inject the insulin as rapidly as possible. One handed holds on all but the smallest of dogs aren't very secure and are likely to just freak them out and you'll lose even more trust.