Hi Alicia, I have a 19 month old with CF. I'm not sure if you're talking about an inhaler or nebulizer. We didn't have to do many nebs either until the last few months. Now we do 4 treatments a day.
Try letting her play with the mask, put it on you, on a stuffed animal, etc. Try to make a game of it. I sit right in front of the tv with a favorite movie or cartoon on to distract my son, or have daddy sit right in front of us to play with him. You can start by holding it a few inches from her face, then as she becomes more used to it, start holding it closer and closer, until she lets you hold it to her face. My son still won't let me use the elastic strap though, I just hold it for him. Just try to make it a fun game, let her play with the equipment, let her try to do it herself. And try to distract her with songs or movies or another person making funny faces or something. My son was awful but now he's pretty good about it, he even holds it to his face by himself sometimes. If the mask thing just isn't working, try just using the mouthpiece and hold it a few inches away, letting the med blow by her nose and mouth. But the mask is more effective, more med goes into the lungs instead of the air.
Same goes for the inhaler, I had to make it a game. I let him play with it and do it to me or a teddy bear. I tell him "Oh my, look at what a big boy you are!" and everytime he lets me do it I make a big deal of it, lots of clapping and "Yay!"I'll also let him play with things he usually doesn't get to, like my cell phone, just when we're doing treatments, to keep him distracted.
It does get easier as they get more used to it, even though sometimes they just don't want to be bothered and would rather play. Then I have to fight a little. But, like other people have said, my doc said to do it while he sleeps if I need to. He also said that if he's crying he's taking in these really deep breaths and inhaling the med deep down in the lungs, so not to feel too bad if he cries. Even though he may be taking less breaths, as Luke said, we're using a mask so the med is sitting there waiting for him to take a deep breath again.
If you let her play with the equipment, let her after every treatment, so she knows if she just sits still for a few minutes she gets to play with it. Unless you have an extra to let her play with while you're doing it. I usually don't let my son play with it before hand because I don't want him to get germs all over it from me or the stuffed animals or floor or whatever, then put it on his face and have him breath in all those germs.
Anyways, sorry so long, I just wanted to share what helps with my son. I had this problem a few months ago and was on here asking everyone for tips too. Basically, make it a game, so its not so scary. Keep her distracted. Make sure she's not hungry or wet before hand so she'll sit still. And it helps if they're tired or sleeping. Just do it gradually and eventually she'll get used to it.