We are working on teaching the dumbbell hold. I got a hard plastic dumbbell but it seems slippery and hard for her to hold. Should I teach her with the wooden style instead? 

I don't teach hold with a dumbbell, I teach with a piece of PVC first and then a wooden dowel.

Since teaching the hold can be mildly stressful I don't like to associate any of the stress with the actual item my dog will be retrieving in real life or competition. I don't start with wood because it tends to promote chewing more than PVC.

We offer a starter kit and I follow the steps and techniques shown in the Retrieve video we did with Michael Ellis.

You can teach with the dumbbell, that's how we used to do it but have found that isolating the hold away from the dumbbell makes what we are asking more clear for the dog.