Would the older sister, even though she is young, consider being in the room and maybe wearing a mask too to show her little sister that it's fun and cool. Does your daughter use a mask? They have cool ones that have designs/shapes and such onthem. Maybe if she has a favorite movie, toy or game you can use that. All in all though, I think a lot of success stories I have heard come from an older sibling "doing" the nebulizer (for a few minutes with no meds) first and then the younger one does it, or they both wear masks at the same time and lay together watching a movie or something. Just an idea, I have a husband with CF, not a child... but I do know that older siblings can be really impressionable.
It might help the older one too, maybe she won't be so upset if she gets to be involved in helping out.
It might help the older one too, maybe she won't be so upset if she gets to be involved in helping out.