I would ask the respiratory therapist to show <i>me</i> the literature from which she is getting her information. Just because she has a white coat on doesn't make her right. Maybe she graduated last in her class.
The Cystic Foundation (as someone else pointed out) has several approved methods of sterilizing and boiling is one of them. Ya think they'd know.
The reason that you periodically have to use vinegar in addition is to dissolve the calcium deposits that are left behind especially if you have hard water. You might notice a chalky film left on your nebulizers. Vinegar alone is no longer an approved method for the actual sterilizing is because -- it doesn't kill pseudomonas (and maybe other bugs).
I boil sometimes but our water is so hard, the nebulizers stop working pretty quickly. Although someone on this site had a good suggestion by recommending putting a tablespoon of vinegar in the water while it's boiling.
I use the baby bottle sterilizer after each use. Then I use Control III at the end of the day and rinse with sterile (boiled water). I also use Control III because I also have to clean the Flutter which you cannot boil.