Zappy had asthma. Lien Animal Clinic had me order a very small (human) mask that fit on the inhaler. She got used to it very quickly because her favorite treat was in the mask.
Dr. Fritzler was the one that said to start by just put a treat in the mask several times a day. Then put the treat their and squeeze the inhaler. Zappy had to put her face into the mask to get the treat, so it worked. The first couple of times I squeezed the inhaler she was surprised, but got used to it very quickly. The treat/positive reward was the key.